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{{About|the fastener|the screw as a simple machine|Screw (simple machine)|other uses|Screw (disambiguation)}}
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[[File:screws.jpg|frame|Screws come in a variety of shapes and sizes for different purposes. [[Quarter (U.S. coin)|U.S. quarter coin]] (diameter 24 mm) shown for scale.]]
 
A '''screw''', or '''bolt''', is a type of [[fastener]] characterized by a [[helix|helical]] ridge, known as an ''external thread'' or just ''[[Screw thread|thread]]'', wrapped around a cylinder.  Some screw threads are designed to mate with a complementary thread, known as an ''internal thread'', often in the form of a [[nut (hardware)|nut]] or an object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted.  The most common uses of screws are to hold objects together and to position objects.
 
A screw will always have a ''head'', which is a specially formed section on one end of the screw that allows it to be turned, or ''driven''. Common tools for driving screws include [[screwdriver]]s and [[wrench]]es. The head is usually larger than the body of the screw, which keeps the screw from being driven deeper than the length of the screw and to provide a ''[[bearing surface]]''. There are exceptions; for instance, carriage bolts have a domed head that is not designed to be driven; [[set screw]]s often have a head smaller than the outer [[diameter]] of the screw; J-bolts have a J-shaped head which is not designed to be driven, but rather is usually sunk into concrete allowing it to be used as an anchor bolt. The cylindrical portion of the screw from the underside of the head to the tip is known as the ''shank''; it may be fully threaded or partially threaded.<ref>{{harvnb|Smith|1990|p=39}}.</ref> The distance between each thread is called the "pitch".
 
The majority of screws are tightened by [[clockwise and counterclockwise|clockwise]] rotation, which is termed a ''right-hand thread''; a common [[mnemonic device]] for remembering this when working with screws or bolts is "righty-tighty, lefty-loosey." Screws with left-hand threads are used in exceptional cases. For example, when the screw will be subject to counterclockwise torque (which would work to undo a right-hand thread), a left-hand-threaded screw would be an appropriate choice. The left side [[Bicycle pedal#Attachment|pedal]] of a [[bicycle]] has a left-hand thread.
 
More generally, screw may mean any helical device, such as a clamp, a [[micrometer]], a ship's propeller or an [[Archimedes' screw]] water pump.
 
==Differentiation between bolt and screw==
[[File:Bolt (PSF).png|thumb|A carriage bolt with square nut]]
[[File:DIN6914 UNI5587.jpg|thumb|upright|150px|A structural bolt with a hex nut and washer.]]
 
There is no universally accepted distinction between a screw and a bolt. ''[[Machinery's Handbook]]'' describes the distinction as follows:
 
{{quote|A bolt is an externally threaded fastener designed for insertion through holes in assembled parts, and is normally intended to be tightened or released by torquing a nut. A screw is an externally threaded fastener capable of being inserted into holes in assembled parts, of mating with a preformed internal thread or forming its own thread, and of being tightened or released by torquing the head. An externally threaded fastener which is prevented from being turned during assembly and which can be tightened or released only by torquing a nut is a bolt. (Example: round head bolts, track bolts, plow bolts.) An externally threaded fastener that has thread form which prohibits assembly with a nut having a straight thread of multiple pitch length is a screw. (Example: wood screws, tapping screws.)<ref>{{harvnb|Oberg|Jones|Horton|Ryffel|2000|p=1492}}.</ref>}}
 
This distinction is consistent with [[ASME B18.2.1]] and some dictionary definitions for ''screw''<ref>{{cite web | title = Cambridge Dictionary of American English | publisher = Cambridge University Press | url = http://dictionary.cambridge.org/define.asp?key=screw*1+0&dict=A | accessdate = 2008-12-03}}</ref><ref>{{cite web | title = allwords | url = http://www.allwords.com/query.php?SearchType=3&Keyword=screw&goquery=Find+it%21&Language=ENG | accessdate = 2008-12-03}}</ref> and ''bolt''.<ref>{{cite web | title = Merriam Webster Dictionary bolt | url = http://www.merriam-webster.com/dictionary/bolt | accessdate = 2008-12-03}}</ref><ref>{{cite web | title = Compact Oxford English Dictionary bolt | publisher = Oxford | url = http://www.askoxford.com/concise_oed/bolt_1?view=uk | accessdate = 2008-12-03}}</ref><ref>{{cite web | title = Cambridge Advanced Learner's Dictionary bolt | publisher = Cambridge University Press | url = http://dictionary.cambridge.org/define.asp?key=8680&dict=CALD | accessdate = 2008-12-03}}</ref>
 
The issue of what is a screw and what is a bolt is not completely resolved with ''Machinery's Handbook'' distinction, however, because of confounding terms, the ambiguous nature of some parts of the distinction, and usage variations.<ref>{{cite web|title=The Fastener Resource Center - Know your Bolts|url=http://www.fastenerexperts.com/bolt-guide/
|accessdate = 2011-03-13}}</ref>{{failed verification|date=September 2013}} Some of these issues are discussed below:
 
=== Machine screws ===
ASME standards specify a variety of "Machine Screws"<ref>{{harvnb|Oberg|Jones|Horton|Ryffel|2000|pp=1568–1598}}.</ref> in diameters ranging up to {{convert|0.75|in|mm|2|abbr=on}}.  These fasteners are often used with nuts as well as driven into tapped holes.  They might be considered a screw or a bolt based on the ''Machinery's Handbook'' distinction.  In practice, they tend to be mostly available in smaller sizes and the smaller sizes are referred to as screws or less ambiguously as machine screws, although some kinds of machine screw can be referred to as stove bolts.
 
=== Hex cap screws ===
ASME standard B18.2.1-1996 specifies Hex Cap Screws that range in size from {{convert|0.25|–|3|in|mm|2|abbr=on}} in [[diameter]].  These fasteners are very similar to hex bolts.  They differ mostly in that they are manufactured to tighter tolerances than the corresponding bolts.  ''Machinery's Handbook'' refers parenthetically to these fasteners as "Finished Hex Bolts".<ref>{{harvnb|Oberg|Jones|Horton|Ryffel|2000|p=1496}}.</ref> Reasonably, these fasteners might be referred to as bolts, but based on the US government document ''Distinguishing Bolts from Screws'', the US government might classify them as screws because of the tighter tolerance.<ref>{{cite web|title=Distinguishing Bolts from Screws page 7|url=http://www.cbp.gov/linkhandler/cgov/trade/legal/informed_compliance_pubs/icp013.ctt/icp013.pdf|accessdate = 2009-01-13}}</ref> In 1991 responding to an influx of counterfeit fasteners Congress passed PL 101-592<ref>[http://ts.nist.gov/WeightsAndMeasures/fqaregs2.cfm Fastener Quality Act (FQA): Text of the Fastener Quality Act - fqaregs2<!-- generated title -->]</ref> "Fastener Quality Act" This resulted in the rewriting of specifications by the ASME B18 committee. B18.2.1<ref>[http://catalog.asme.org/Codes/PrintBook/B1821_1996_Square_Hex_Bolts.cfm B18.2.1 - 1996 Square and Hex Bolts and Screws, Inch Series - Print-Book<!-- Bot generated title -->]</ref> was re-written and as a result they eliminated the "Finished Hex Bolts" and renamed them the "Hex Cap Screw"—a term that had existed in common usage long before, but was now also being codified as an official name for the ASME B18 standard.
 
=== Lug bolts and head bolts ===
These terms refer to fasteners that are designed to be threaded into a tapped hole that is in part of the assembly and so based on the ''Machinery's Handbook'' distinction they would be screws.  Here common terms are at variance with ''Machinery's Handbook'' distinction.<ref>{{cite web|title=autorepair.com Glossary - lug bolt|url=http://autorepair.about.com/library/glossary/bldef-900.htm|accessdate = 2009-01-13}}</ref><ref>{{cite web|title=autozone.com Glossary - head bolt|url=http://www.autozone.com/autozone/repairinfo/common/repairInfoMain.jsp?leftNavPage=glossary&startLetter=h&targetPage=glossarySelected|accessdate = 2010-10-13}}</ref>
 
=== Lag screw ===
[[File:Lag screws aka lag bolts 001.png|thumb|Lag screws, also called lag bolts.]]
[[File:Lag screws aka lag bolts 002.png|thumb|Another view.]]
Lag screws, also sometimes called lag bolts, are basically "large wood screws". Square lag screws and hex lag screws are covered by ASME B18.2.1.  A typical lag bolt can range in diameters from 1/4" to 1 1/4", and lengths from 1/4" to 6" or longer, with coarse threads of a wood-screw or sheet-metal-screw threadform (but larger). The head is typically an external hex. The materials are usually carbon steel substrate with a coating of zinc [[galvanization]] (for corrosion resistance). The zinc coating may be bright (electroplated), yellow (electroplated), or dull gray [[hot-dip galvanizing|hot-dip galvanized]]. Lag bolts are used to lag together lumber framing, to lag machinery feet to wood floors, and other heavy carpentry applications. These fasteners are clearly "screws" when defined by the ''Machinery's Handbook'' distinction.  The term "lag bolt" has been replaced by "lag screw" in the ''Machinery's Handbook''.<ref>{{harvnb|Oberg|Jones|Horton|Ryffel|2000|p=1497}}.</ref> However, in the minds of most tradesmen, they are "bolts", simply because they are large, with hex or square heads. In the United Kingdom, lag bolts/screws are known as ''coach screws'' though this can also refer to carriage bolts (round head).
 
=== Government standards ===
The [[US government]] made an effort to formalize the difference between a bolt and a screw because different [[tariffs]] apply to each.<ref name="CBP.gov_bolts-vs-screws">{{Citation |author=U.S. Customs and Border Protection Agency (CBP) |authorlink=U.S. Customs and Border Protection |year=2011 |date=February 2011 |title=What Every Member of the Trade Community Should Know About: Distinguishing Bolts from Screws |series=An Informed Compliance Publication |edition=2011-02 |publisher=CBP.gov |location=Washington, DC, USA |pages= |url=http://www.cbp.gov/linkhandler/cgov/trade/legal/informed_compliance_pubs/icp013.ctt/icp013.pdf |doi= |id= |postscript=.}}</ref> The document seems to have no significant effect on common usage and does not eliminate the ambiguous nature of the distinction between screws and bolts for some threaded fasteners. The document also reflects (although it probably did not originate) significant confusion of terminology usage that differs between the legal/statutory/regulatory community and the fastener industry. The legal/statutory/regulatory wording uses the terms "coarse" and "fine" to refer to the tightness of the [[engineering tolerance|tolerance]] range, referring basically to "high-quality" or "low-quality", but this is a poor choice of terms, because those terms in the fastener industry have a different meaning (referring to [[Screw thread#Coarse versus fine|the steepness of the helix's lead]]).
 
=== Historical issue ===
Old [[United States Standard|USS]] and [[Society of Automotive Engineers|SAE]] standards defined cap screws as fasteners with shanks that were threaded to the head and bolts as fasteners with shanks that were partially unthreaded.<ref name="dyke">{{Citation|title=Dyke's Automobile and Gasoline Engine Encyclopedia page 701|url=http://books.google.com/?id=WqI7AAAAMAAJ&pg=RA1-PA702&lpg=RA1-PA702&dq=sae+uss+screw+standard|accessdate = 2009-01-13|postscript=. | year=1919 | publisher=A.L. Dyke}}</ref> The relationship of this rule to the idea that a bolt by definition takes a nut is clear (because the unthreaded section of the shank, which is called the ''grip'', was expected to pass through the substrate without threading into it). This is now an obsolete distinction.
 
=== Controlled vocabulary versus natural language ===
The distinctions above are enforced in the [[controlled vocabulary]] of [[standards organization]]s. Nevertheless, there are sometimes differences between the controlled vocabulary and the [[natural language]] use of the words by machinists, auto mechanics and others. These differences reflect linguistic evolution shaped by the [[History of technology|changing of technology over centuries]]. The words ''bolt'' and ''screw'' have both existed since before today's modern mix of fastener types existed, and the natural usage of those words has evolved [[retronym]]ously in response to the technological change. (That is, the use of words as names for objects changes as the objects themselves change.) Non-threaded fasteners predominated until the advent of practical, inexpensive screw-cutting in the early 19th century. The basic meaning of the word ''screw'' has long involved the idea of a helical screw thread, but the Archimedes screw and the screw [[gimlet (tool)|gimlet]] (like a corkscrew) preceded the fastener.
 
The word ''bolt'' is also a very old word, and it was used for centuries to refer to metal rods that passed through the substrate to be fastened on the other side, often via nonthreaded means (clinching, forge welding, pinning, wedging, etc.). The connection of this sense to the sense of a door bolt or the [[crossbow]] bolt is apparent. In the 19th century, bolts fastened via screw threads were often called ''screw bolts'' in contradistinction to [[Clinker (boat building)#Fastening the centre-line structure|''clench bolts'']].
 
In common usage, the distinction (not rigorous) is often that screws are smaller than bolts, and that screws are generally tapered while bolts are not. For example, [[cylinder head]] bolts are called "bolts" (at least in North American usage) despite the fact that by some definitions they ought to be called "screws". Their size and their similarity to a bolt that would take a nut seem linguistically to overrule any other factors in this [[natural language|natural]] word choice proclivity.
 
====Other distinctions====
Bolts have been defined as headed fasteners having external threads that meet an exacting, uniform bolt thread specification (such as [[ISO metric screw thread]] M, MJ, [[Unified Thread Standard]] UN, UNR, and UNJ) such that they can accept a non-tapered nut. Screws are then defined as headed, externally threaded fasteners that do not meet the above definition of bolts.{{Citation needed|date=June 2009}}<!-- See the talk page. --> These definitions of screw and bolt eliminate the ambiguity of the ''Machinery's handbook'' distinction.  And it is for that reason, perhaps, that some people favor them.  However, they are neither compliant with common usage of the two words nor are they compliant with formal specifications.
 
A possible distinction is that a screw is designed to cut its own thread; it has no need for access from or exposure to the opposite side of the component being fastened to.  This definition of screw is further reinforced by the consideration of the developments of fasteners such as Tek Screws for roof cladding, self-drilling and self-tapping screws for various metal fastening applications, roof batten screws to reinforce the connection between the roof batten and the rafter, decking screws etc.
On the other hand, a bolt is the male part of a fastener system designed to be accepted by a pre-equipped socket (or nut) of exactly the same thread design.
 
==Types of screw and bolt==<!-- [[Carriage bolt]] redirects here -->
Threaded fasteners either have a tapered shank or a non-tapered shank. Fasteners with tapered shanks are designed to either be driven into a substrate directly or into a pilot hole in a substrate. Mating threads are formed in the substrate as these fasteners are driven in. Fasteners with a non-tapered shank are designed to mate with a nut or to be driven into a tapped hole.
 
===Fasteners with a tapered shank (self-threading screws)===
{| class="wikitable sortable"
|-
! class="unsortable" | !!style="width: 140px" | American name  !!style="width: 140px" | British name !! class="unsortable" | Description
|-
|  || chipboard screw<br />particle board screw ||  || Similar to a drywall screw except that it has a thinner shaft and provides better resistance to pull-out in particle board, while offset against a lower shear strength. The threads on particle board screws are asymmetrical.
|-
|  || {{visible anchor|concrete screw}}<br />Tapcons<br />masonry screw<br />confast screw<br />blue screw<br />self-tapping screw<br />Titen ||  || A stainless or carbon steel screw for fastening wood, metal, or other materials into concrete or masonry. Concrete screws are commonly blue in color, with or without corrosion coating.<ref>Source: http://www.confast.com/articles/tapcon-screw.aspx</ref> They may either have a Phillips flat head or a slotted hex washer head. Heads sizes range from {{convert|0.1875|to|0.375|in|mm|3|abbr=on}} and lengths from {{convert|1.25|to|5|in|mm|0|abbr=on}}. Typically an installer uses a [[hammer drill]] to make a pilot hole for each concrete screw.
|-
|  || deck screw ||  || Similar to drywall screw except that it has improved corrosion resistance and is generally supplied in a larger gauge. Most deck screws have a type-17 (auger type) thread cutting tip for installation into decking materials. They have bugle heads that allows the screw to depress the wood surface without breaking it.
|-
| [[File:Stockschraube.jpg|30px]]<!-- I know it's not quite right because one end has a machine thread on it, but it's close enough until a better image is taken --> || double ended screw<br />dowel screw<br>hanger bolt ||  || Similar to a wood screw but with two pointed ends and no head, used for making hidden joints between two pieces of wood. <br>A hanger bolt has wood screw threads on one end and machine threads on the other. A hanger bolt is used when it is necessary to fasten a metal part to a wood surface.
|-
| [[File:Screw.agr.jpg|120px]] || drywall screw ||  || Specialized screw with a bugle head that is designed to attach drywall to wood or metal studs, however it is a versatile construction fastener with many uses. The diameter of drywall screw threads is larger than the shaft diameter.
|-
| [[File:Eye bolt wood thread.jpg|80px]] || eye screw<br />screw eye  || || Screw with a looped head. Larger ones are sometimes called lag eye screws. Designed to be used as attachment point, particularly for something that is hung from it.
|-
| [[File:Tire-fond cropped.JPG|120px]] || lag bolt<br />lag screw<ref>{{cite web | title = coach screw definition | publisher = dictionary.com | url = http://dictionary.reference.com/browse/coach+screw?qsrc=2446 | accessdate = 2010-01-19}}</ref> || coach screw || Similar to a wood screw except that it is generally much larger running to lengths up to {{convert|15|in|mm|0|abbr=on}} with diameters from {{convert|0.25|–|0.5|in|mm|2|abbr=on}} in commonly available (hardware store) sizes (not counting larger mining and civil engineering lags and lag bolts) and it generally has a hexagonal drive head. Lag bolts are designed for securely fastening heavy timbers ([[Timber framing|post and beams]], timber railway trestles and bridges) to one another, or to fasten wood to masonry or concrete.
 
Lag bolts are usually used with an expanding insert called a lag in masonry or concrete walls, the lag manufactured with a hard metal jacket that bites into the sides of the drilled hole, and the inner metal in the lag being a softer alloy of lead, or zinc alloyed with soft iron. The coarse thread of a lag bolt and lag mesh and deform slightly making a secure near water tight anti-corroding mechanically strong fastening.
|-
| [[File:Mirror Screws.jpg|120px]]|| mirror screw || || This is a flat-head wood screw with a tapped hole in the head, which receives a screw-in chrome-plated cover. It is usually used to mount a mirror.
|-
| [[File:Phillips screw.jpg|120px]] || {{visible anchor|sheet metal screw}}  ||  || Has sharp threads that cut into a material such as sheet metal, plastic or wood. They are sometimes notched at the tip to aid in chip removal during thread cutting. The shank is usually threaded up to the head. Sheet metal screws make excellent fasteners for attaching metal hardware to wood because the fully threaded shank provides good retention in wood.
|-
|  || Twinfast screw ||  || A Twinfast screw is a type of screw with two threads (i.e. a [[lead (engineering)|twin-start screw]]), so that it can be driven twice as fast as a normal (i.e. single-start) screw with the same pitch.<ref>{{Citation | last = Soled | first = Julius | title = Fasteners handbooks | page = 151 | publisher = Reinhold | year = 1957 | url = http://books.google.com/books?id=8OdSAAAAMAAJ&pg=PA151 | postscript =.}}</ref> Dry wall screws designated as fine are the most common screws to use the twinfast style of threads.<ref>{{cite web | url=http://www.mutualscrew.com | title = Fine thread drywall screws| publisher = Mutual Screw & Fastener Supply | accessdate = 2011-03-16}}</ref>
|-
| [[File:Screw for wood.JPG|120px]] || {{visible anchor|wood screw}} || || A metal screw with a sharp point designed to attach two pieces of wood together. Wood screws are commonly available with flat, pan or oval-heads. A wood screw generally has a partially unthreaded shank below the head. The unthreaded portion of the shank is designed to slide through the top board (closest to the screw head) so that it can be pulled tight to the board it is being attached to.
|-
| ||Security head screw|| || These screws are use for security purpose. The head of this type of screw is impossible to reverse. It requires special tools or mechanisms like spanners, tri-wings, torxes, square drivers, etc. In some screws, the head can be removed by breaking it after installing the screw.
|}
 
===Fasteners with a non-tapered shank===
{| class="wikitable sortable"
|-
! class="unsortable" | !!style="width: 140px" | American name  !!style="width: 140px" | British name !! class="unsortable" | Description
|-
| [[File:AnchorBolt M12 01.jpg|120px]] || anchor bolt <!-- J-bolt? --> || || A special type of bolt that is set in wet concrete, with the screw threads protruding above the concrete surface.
|-
|  || breakaway bolt || || A breakaway bolt is a bolt with a hollow threaded shank, which is designed to break away upon impact. Typically used to fasten fire hydrants, so they will ''break away'' when hit by a car. Also used in aircraft to reduce weight.
|-
| [[File:Vis 6 pans creux coupee.JPG|thumb|150px|Narrow definition]] [[File:Tornillo (Tipos de cabeza).png|thumb|150px|Wide definition]] || {{visible anchor|cap screw}} ||  || The term cap screw  refers to many different things at different times and places. Currently, it most narrowly refers to a style of head (see the gallery below). More broadly, and more commonly, it refers to the group of screws: shoulder screws, hex heads, counter-sunk heads, button heads, and fillister heads. In the US, cap screws are defined by ASME B18.6.2 and ASME B18.3.<ref>{{harvnb|Oberg|2000|pp=1599–1605}}.</ref><ref>{{Citation | last = Samuel | first = Andrew | title = Introduction to Engineering Design | publisher = Butterworth-Heinemann | location = Oxford | year = 1999 | page = 213 | url = http://books.google.com/books?id=xxuyvQR34O4C&pg=PA213 | isbn = 0-7506-4282-3}}</ref> In the past, the term ''cap screw'', in general, referred to screws that were supposed to be used in applications where a nut was not used, however the characteristics that differentiated it from a bolt vary over time. In 1910, Anthony defined it as screw with a hex head that was thicker than a bolt head, but the distance across the flats was less than a bolt's.<ref>{{Citation | last = Anthony | first = Gardner Chase | title = Machine Drawing | page = 16 | publisher = D. C. Heath | year = 1910 | url = http://books.google.com/books?id=XUM1AAAAMAAJ&pg=PA16 | postscript =.}}</ref> In 1913, Woolley and Meredith defined them like Anthony, but gave the following dimensions: hex head cap screws up to and including {{convert|7/16|in|mm|4}} have a head that is {{convert|3/16|in|mm|4}} larger than the shank diameter; screws greater than {{convert|1/2|in|mm|1}} in diameter have a head that is {{convert|1/4|in|mm|2}} larger than the shank. Square head cap screws up to and including {{convert|3/4|in|mm|2}} have a head {{convert|1/8|in|mm|3}} larger than the shank; screws larger than {{convert|3/4|in|mm|2}} have a head {{convert|1/4|in|mm|2}} larger than the shank.<ref>{{Citation | last = Woolley | first = Joseph William | last2 = Meredith | first2 = Roy Brodhead | title = Shop sketching | pages = 40–41 | publisher = McGraw-Hill | year = 1913 | url = http://books.google.com/books?id=b-lKAAAAMAAJ&pg=PA40 | postscript =.}}</ref> In 1919, Dyke defined them as screws that are threaded all the way to the head.<ref name="dyke"/>
 
A socket cap screw, also known as a ''socket head capscrew'', ''socket screw'', "set screw" or ''Allen bolt'', is a type of cap screw with a cylindrical head and hexagonal drive hole.  The term ''socket head capscrew'' typically refers to a type of threaded fastener whose head diameter is [[Real versus nominal value|nominally]] 1.5 times that of the screw shank ([[major diameter|major]]) diameter, with a head height equal to the shank diameter (1960 series design). [[forging|Forged]] [[heat treat|heat-treated]] [[alloy]] examples are high strength fasteners intended for the most demanding mechanical applications, with special alloy formulations available that are capable of maintaining strength at temperatures in excess of 1000 degrees F (587 degrees C).
 
In addition to the 1960 series design, other head designs include low head, button head and flat head, the latter designed to be seated into [[countersink|countersunk]] holes.  A [[hex key]] (sometimes referred to as an ''Allen wrench'' or ''Allen key'') or ''[[hex driver]]'' is required to tighten or loosen a socket screw. Socket head capscrews are commonly used in assemblies that do not provide sufficient clearance for a conventional wrench or [[socket wrench|socket]].
|-
| [[File:Carriage bolts.jpg|30px]] || carriage bolt || Cup head bolt, Coach bolt || A carriage bolt, also known as a coach bolt, has a domed or countersunk head, and the shank is topped by a short square section under the head. The square section grips into the part being fixed (typically wood), preventing the bolt from turning when the nut is tightened. A rib neck carriage bolt has several longitudinal ribs instead of the square section, to grip into a metal part being fixed.
|-
| [[File:Elevatorbolt.jpg|30px]] || elevator bolt ||  || An elevator bolt is a bolt similar to a carriage bolt, except the head is thin and flat. There are many variations. Some do not have a square base, but rather triangular sections of the flat head are folded down to form "fangs" that cut into wood and hold it secure.<ref>[http://myword.info/definition.php?id=el_head_1-a The Meaning of "elevator head"]</ref>
|-
|  || eye bolt ||  || An eye bolt is a bolt with a looped head.<!-- Some have tapered threads -->
|-
| [[File:Bout.jpg|120px]] || hex cap screw<br />hex bolt ||  || A hex cap screw is a cap screw with a hexagonal head, designed to be driven by a wrench (spanner). An ASME B18.2.1 compliant cap screw has somewhat tighter tolerances than a hex bolt for the head height and the shank length. The nature of the tolerance difference allows an ASME B18.2.1 hex cap screw to always fit where a hex bolt is installed but a hex bolt could be slightly too large to be used where a hex cap screw is designed in.
|-
| [[File:100 TPI fine adjustment screw with close up, Oct 2012.jpg|80px]] || [[Fine adjustment screw]] ||  || The term fine adjustment screw typically refers to screws with threads from 40-100 TPI (Threads Per Inch) (0.5mm to 0.2mm pitch) and ultra fine adjustment screw has been used to refer to 100-254 TPI (0.2mm to 0.1mm pitch).  These screws are most frequently used in applications where the screw is used to control fine motion of an object.
|-
|  || machine screw ||  || A machine screw is generally a smaller fastener (less than {{convert|1/4|in|mm|2}} in diameter) threaded the entire length of its shank that usually has a recessed drive type (slotted, Phillips, etc.).  Machine screws are also made with socket heads (see above), in which case they may be referred to as socket head machine screws.
|-
| || plow bolt || || A plow bolt is bolt similar to a carriage bolt, except the head is flat or concave, and the underside of the head is a cone designed to fit in a countersunk recess. There are  many variations, with some not using a square base, but rather a key, a locking slot, or other means. The recess in the mating part must be designed to accept the particular plow bolt.  ASME B18.9 standard recommends a No. 3 head (round countersunk head square neck) plow bolts and No. 7 head (round countersunk reverse key head) plow bolts for new designs.  The necessary dimensions for the head styles can be found in the standard. <ref>{{Harvnb|Colvin|Stanley|1914|p=569}}.</ref><ref>{{Citation | title = Plow bolts | url = http://www.masterbolt.com/plow_bolts.html | accessdate = 2008-12-25 | postscript =.}}</ref><ref>[http://myword.info/definition.php?id=pl_head_1-a The Meaning of "plow head, plow bolt"] at MyWord.info</ref>
|-
| [[File:Vis-auto-foreuse.jpeg|120px]] || self-drilling screw<br />Teks screw ||  || Similar to a sheet metal screw, but it has a drill-shaped point to cut through the substrate to eliminate the need for drilling a pilot hole. Designed for use in soft steel or other metals. The points are numbered from 1 through 5, the larger the number, the thicker metal it can go through without a pilot hole. A 5 point can drill a {{convert|0.5|in|mm|1|abbr=on}} of steel, for example.
|-
| [[File:Vis-auto-taraudeuse.jpeg|120px]] || self-tapping machine screw ||  || A self-tapping machine screw is similar to a machine screw except the lower part of the shank is designed to cut threads as the screw is driven into an untapped hole. The advantage of this screw type over a self-drilling screw is that, if the screw is reinstalled, new threads are not cut as the screw is driven.
|-
| || set bolt || tap bolt || A bolt that is threaded all the way to the head. An ASME B18.2.1 compliant set/tap bolt has the same tolerances as an ASME B18.2.1 compliant hex cap screw.
|-
| [[File:Setscrews (PSF).png|60px]] || [[set screw]] || grub screw || A set screw is generally a headless screw but can be any screw used to fix a rotating part to a shaft. The set screw is driven through a threaded hole in the rotating part until it is tight against the shaft.  The most often used type is the socket set screw, which is tightened or loosened with a hex key.
|-
| || shoulder bolt<br />shoulder screw || stripper bolt || A shoulder screw differs from machine screws in that the shank is held to a precise diameter, known as the ''shoulder'', and the threaded portion is smaller in diameter than the shoulder. Shoulder screw specifications call out the shoulder diameter, shoulder length, and threaded diameter; the threaded length is fixed, based on the threaded diameter, and usually quite short. Shoulder screws can be manufactured in many materials such as [[alloy]] [[heat treat|heat-treated]] [[steel]] for maximum strength and wear resistance and stainless steel for its corrosion-resistance and non-magnetic properties. Common applications for shoulder screws include rotating [[mechanism (engineering)|mechanism joints]], [[linkage (mechanical)|linkage pivots]], and guides for the [[stripper plate]] of a [[die (manufacturing)|metal forming die]] set.  In the latter application, the term stripper bolt is often substituted. Stainless steel shoulder screws are used with linear motion devices such as bearings, as guides and as pivots in electronic and other critical mechanical applications.
|-
|  || stove bolt || || A stove bolt is a type of machine screw that has a round or flat head and is threaded to the head. They are usually made of low grade steel, have a slot or Phillips drive, and are used to join sheet metal parts using a hex or square nut.<ref>Huth, pp. 166–167.</ref>
|-
| || tension control bolt || || A tension control bolt (TC bolt) is a heavy duty bolt used in steel frame construction. The head is usually domed and is not designed to be driven. The end of the shank has a spline on it which is engaged by a special power wrench which prevents the bolt from turning while the nut is tightened. When the appropriate torque is reached the spline shears off.
|-
| || thread rolling screws ||  || These have a lobed (usually triangular) cross-section. They form threads in a pre-existing hole in the mating workpiece by pushing the material outward during installation. In some cases the properly prepared hole in sheetmetal uses an extruded hole. The extrusion forms a lead-in and extra thread length for improved retention. Thread rolling screws are often used where loose chips formed by a thread cutting operation cannot be tolerated.
|}
 
===Fasteners with built in washers===
A fastener with a built in [[Washer (hardware)|washer]] is called a SEM or SEMS, short for pre-as'''SEM'''bled.<ref>{{cite web|title=All About Screws|url=http://www.elexp.com/tips/AllAboutScrews.pdf|publisher=Curious Inventor|accessdate=17 October 2013}}</ref><ref>{{cite web|title=Glossary|url=http://www.boltscience.com/pages/glossary.htm#s|accessdate=17 October 2013}}</ref>  It could be fitted on either a tapered or non-tapered shank.
 
===Other threaded fasteners===
 
==== Superbolt, or multi-jackbolt tensioner ====
A superbolt, or [[multi-jackbolt tensioner]] is an alternative type of fastener that retrofits or replaces existing nuts, bolts, or studs. Tension in the bolt is developed by torquing individual jackbolts, which are threaded through the body of the nut and push against a hardened washer.  Because of this, the amount of torque required to achieve a given preload is reduced.  Installation and removal of any size tensioner is achieved with hand tools, which can be advantageous when dealing with large diameter bolting applications.
 
====Hanger screw or hanger bolt====
A hanger screw is a headless fastener that has machine screw threads on one end and self-tapping threads on the other designed to be driven into wood or another soft substrate.  Often used for mounting legs to tables. Also known as a dowel screw.
 
===List of abbreviations for types of screws===
These abbreviations have [[jargon]] currency among fastener specialists (who, working with many screw types all day long, have need to abbreviate repetitive mentions). The smaller basic ones can be built up into the longer ones; for example, if you know that "FH" means "flat head", then you may be able to parse the rest of a longer abbreviation containing "FH".
 
These abbreviations are not universally standardized across corporations; each corporation can coin their own. The more obscure ones may not be listed here.
 
The extra spacing between linked terms below helps the reader to see the correct parsing at a glance.
 
{| class="wikitable"
! scope="col" style="width: 15%;" | Abbreviation
! scope="col" style="width: 35%;" | Expansion
! scope="col" style="width: 50%;" | Comment
|-
| BH || [[screw#Screw head shapes|button head]] ||
|-
| BHCS || [[screw#Screw head shapes|button head]] &nbsp; cap screw ||
|-
| BHMS || [[screw#Screw head shapes|button head]] &nbsp; [[screw#Machine screws|machine screw]] ||
|-
| CS || cap screw ||
|-
| FH || [[screw#Screw head shapes|flat head]] ||
|-
| FHP || [[screw#Screw head shapes|flat head]] &nbsp; [[list of screw drives#Phillips|Phillips]] ||
|-
| FHPMS || [[screw#Screw head shapes|flat head]] &nbsp; [[list of screw drives#Phillips|Phillips]] &nbsp; [[screw#Machine screws|machine screw]] ||
|-
| FT || full [[screw thread|thread]] || In other words, zero grip length (the whole shank is threaded)
|-
| HHCS || [[screw#Hex cap screws|hex head &nbsp; cap screw]] ||
|-
| MS || [[screw#Machine screws|machine screw]] ||
|-
| OH || [[screw#Screw head shapes|oval head]] ||
|-
| PH || [[list of screw drives#Phillips|Phillips head]] ||
|-
| RH || [[screw#Screw head shapes|round head]] ||
|-
| RHMS || [[screw#Screw head shapes|round head]] &nbsp; [[screw#Machine screws|machine screw]] ||
|-
| RHP || [[screw#Screw head shapes|round head]] &nbsp; [[list of screw drives#Phillips|Phillips]] ||
|-
| RHPMS || [[screw#Screw head shapes|round head]] &nbsp; [[list of screw drives#Phillips|Phillips]] &nbsp; [[screw#Machine screws|machine screw]] ||
|-
| SBHCS || [[list of screw drives#Hex socket|socket]] &nbsp; [[screw#Screw head shapes|button head]] &nbsp; cap screw ||
|-
| SBHMS || [[list of screw drives#Hex socket|socket]] &nbsp; [[screw#Screw head shapes|button head]] &nbsp; [[screw#Machine screws|machine screw]] ||
|-
| SH || [[list of screw drives#Hex socket|socket head]] || Although "socket head" could logically refer to almost any [[gender of connectors and fasteners|female]] drive, it refers by convention to [[list of screw drives#Hex socket|hex socket head]] unless further specified
|-
| SHCS || [[list of screw drives#Hex socket|socket head]] &nbsp; cap screw ||
|-
| SHSS || [[list of screw drives#Hex socket|socket head]] &nbsp; [[set screw]] ||
|-
| SS || [[set screw]] ||
|-
| STS || [[self-tapping screw]] ||
|-
|}
 
==Materials==
Screws and bolts are usually made of [[steel]].
Where great resistance to weather or corrosion is required, like in very small screws or medical implants, materials such as [[stainless steel]], [[brass]], [[titanium]], [[bronze]], silicon bronze or monel may be used.
 
[[Galvanic corrosion]] of dissimilar metals can be prevented (using [[aluminium|aluminum]] screws for double-glazing tracks for example) by a careful choice of material.
Some types of plastic, such as [[nylon]] or [[polytetrafluoroethylene]] (PTFE), can be threaded and used for fastenings requiring moderate strength and great resistance to corrosion or for the purpose of electrical [[Electrical insulation|insulation]].
 
Often a surface coating is used to protect the fastener from corrosion (e.g. bright zinc plating for steel screws), to impart a decorative finish (e.g. [[japanning]]) or otherwise alter the surface properties of the base material.
 
Selection criteria of the screw materials include: size, required strength, resistance to corrosion, joint material, cost and temperature.
 
==Bolted joints==
[[File:Rustybolt th.jpg|thumb|right|Rusty hexagonal bolt heads]]
{{Main|Bolted joint}}
 
The [[American Institute of Steel Construction]] ([[AISC]]) 13th Edition Steel Design Manual section 16.1 chapter J-3 specifies the requirements for bolted structural connections. Structural bolts replaced rivets due to decreasing cost and increasing strength of structural bolts in the 20th century. Connections are formed with two types of joints: slip-critical connections and bearing connections. In slip-critical connections, movement of the connected parts is a serviceability condition and bolts are tightened to a minimum required pretension. Slip is prevented through friction of the "faying" surface, that is the plane of shear for the bolt and where two members make contact. Because friction is proportional to the normal force, connections must be sized with bolts numerous and large enough to provide the required load capacity. However, this greatly decreases the shear capacity of each bolt in the connection. The second type and more common connection is a bearing connection. In this type of connection the bolts carry the load through shear and are only tightened to a "snug-fit". These connections require fewer bolts than slip-critical connections and therefore are a less expensive alternative. Slip-critical connections are more common on flange plates for beam and column splices and moment critical connections. Bearing type connections are used in light weight structures and in member connections where slip is not important and prevention of structural failure is the design constraint. Common bearing type connections include: shear tabs, beam supports, gusset plates in trusses.
 
==Mechanical classifications==<!-- [[Property class]] & [[Grade (fasteners)]] redirect here -->
The numbers stamped on the head of the bolt are referred to the grade of the bolt used in certain application with the strength of a bolt. High-strength steel bolts usually have a hexagonal head with an [[International Organization for Standardization|ISO]] strength rating (called ''property class'') stamped on the head. And the absence of marking/number indicates a lower grade bolt with low strength. The property classes most often used are 5.8, 8.8, and 10.9. The number before the point is the [[ultimate tensile strength]] in [[megapascal|MPa]] divided by 100. The number after the point is 10 times the ratio of tensile yield strength to ultimate tensile strength. For example, a property class 5.8 bolt has a nominal (minimum) ultimate tensile strength of 500 MPa, and a tensile yield strength of 0.8 times ultimate tensile strength or 0.8(500) = 400 MPa.
 
Ultimate tensile strength is the stress at which the bolt fails. Tensile yield strength is the stress at which the bolt will receive a permanent set (an elongation from which it will not recover when the force is removed) of 0.2% [[yield strength#Definition|offset strain]]. When elongating a fastener prior to reaching the yield point, the fastener is said to be operating in the elastic region; whereas elongation beyond the yield point is referred to as operating in the plastic region, since the fastener has suffered permanent plastic deformation.
 
Mild steel bolts have property class 4.6. High-strength steel bolts have property class 8.8 or above.
 
The same type of screw or bolt can be made in many different grades of material. For critical high-tensile-strength applications, low-grade bolts may fail, resulting in damage or injury. On SAE-standard bolts, a distinctive pattern of marking is impressed on the heads to allow inspection and validation of the strength of the bolt. However, low-cost [[counterfeit]] fasteners may be found with actual strength far less than indicated by the markings. Such inferior fasteners are a danger to life and property when used in aircraft, automobiles, heavy trucks, and similar critical applications.
 
=== Inch ===
[[SAE J429]] defines the bolt grades for inch-system sized bolts and screws. It defines them by ''grade'', which ranges from 0 to 8, with 8 being the strongest. Higher grades do not exist within the specification.<ref name="siu">{{Citation | title = Mechanical Methods of Joining | url = http://www.engr.siu.edu/staff2/deruntz/IT208/Chapter%2015%20Mechanical%20Methods%20of%20Joining.ppt | accessdate = 2009-06-06 | postscript =.}}</ref><ref>{{harvnb|Smith|1990|p=54}}.</ref> SAE grades 5 and 8 are the most common.
 
{| class="wikitable collapsible collapsed" width="100%" border="1" style="text-align:center"
! colspan=10 | Head markings and properties for inch-system hex-head cap screws<ref name="boltdepot">{{Citation | title = Bolt grade markings and strength chart | url = http://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx | accessdate = 2009-05-29 | postscript = .}}</ref>
|-
!rowspan=2| Head marking
!rowspan=2| Grade, material and condition
!rowspan=2| Nominal size range (in)
!colspan=2| [[ultimate tensile strength|Proof strength]] 
!colspan=2| Yield strength, min.
!colspan=2| Tensile strength, min.
!rowspan=2| Core hardness ([[Rockwell scale|Rockwell]])
|-
!ksi!!MPa
!ksi!!MPa
!ksi!!MPa
|-
| rowspan=6 | [[File:Hex cap screw-no markings.svg|75px]]
| '''SAE Grade 0'''<ref name="siu"/>
| colspan=8 | Strength and hardness is not specified
|-
| '''SAE grade 1'''<br />'''ASTM A307'''<ref name="fastspec">{{Citation | title = Grade Markings: Carbon Steel Bolts | url = http://www.fastspecinc.com/technical/technical.html | accessdate = 2009-05-30 | postscript =.}}</ref><br />Low carbon steel
| {{Frac|1|4}}–1-{{Frac|1|2}}
| {{convert|33|ksi|MPa|disp=table}}
| colspan=2|
| {{convert|60|ksi|MPa|disp=table}}
| B70–100
|-
| '''ASTM A307 - Grade B'''<ref name="fastspec"/><br />Low or medium carbon steel
| {{Frac|1|4}}–4
| colspan=2|
| colspan=2|
| align=right|60 minimum<br/>100 maximum
| align=right|410 minimum<br/>690 maximum
| B69–95
|-
| rowspan=2 | '''SAE grade 2'''<br />Low or medium carbon steel
| {{Frac|1|4}}–{{Frac|3|4}}
| {{convert|55|ksi|MPa|disp=table}}
| {{convert|57|ksi|MPa|disp=table}}
| {{convert|74|ksi|MPa|disp=table}}
| B80–100<ref name="johndeere">{{Citation | title = Hardware, bulk — Technical information | url = https://jdparts.deere.com/partsmkt/document/english/pmac/36689_fb_BulkHardwareTechInfo.htm | accessdate = 2009-05-30 | postscript =.}}</ref>
|-
| Greater than {{Frac|3|4}}
| {{convert|33|ksi|MPa|disp=table}}
| {{convert|36|ksi|MPa|disp=table}}
| {{convert|60|ksi|MPa|disp=table}}
| B70–100<ref name="johndeere"/>
|-
| '''SAE grade 4'''<ref name="american">{{Citation | title = ASTM, SAE and ISO grade markings and mechanical properties for steel fasteners | url = http://www.americanfastener.com/technical/grade_markings_steel.asp | accessdate = 2009-06-06 | postscript =.}}</ref><br />Medium carbon steel; cold worked
| {{Frac|1|4}}–1-{{Frac|1|2}}
| colspan=2|
| {{convert|100|ksi|MPa|disp=table}}
| {{convert|115|ksi|MPa|disp=table}}
|
|-
| [[File:Hex cap screw-grade 3.svg|75px]] || '''SAE grade 3'''<ref name="fastspec"/><br />Medium carbon steel; cold worked || {{Frac|1|4}}–1
| {{convert|85|ksi|MPa|disp=table}}
| colspan=2|
| {{convert|100|ksi|MPa|disp=table}}
| B70–100
|-
| rowspan=4 | [[File:Hex cap screw-grade 5.svg|75px]] || rowspan=2 | '''SAE grade 5'''<br />Medium carbon steel; quench and tempered
| {{Frac|1|4}}–1 (inc.)
| {{convert|85|ksi|MPa|disp=table}}
| {{convert|92|ksi|MPa|disp=table}}
| {{convert|120|ksi|MPa|disp=table}}
| C25–34<ref name="johndeere"/>
|-
| 1–1-{{Frac|1|2}}
| {{convert|74|ksi|MPa|disp=table}}
| {{convert|81|ksi|MPa|disp=table}}
| {{convert|105|ksi|MPa|disp=table}}
| C19–30<ref name="johndeere"/>
|-
| rowspan=2 | '''ASTM A449 - Type 1'''<ref name="fastspec"/><br />Medium carbon steel; quench and tempered || 1–1-{{Frac|1|2}} (inc.)
| {{convert|74|ksi|MPa|disp=table}}
| colspan=2|
| {{convert|105|ksi|MPa|disp=table}}
| C19–30
|-
| 1-{{Frac|1|2}}–3
| {{convert|55|ksi|MPa|disp=table}}
| colspan=2|
| {{convert|90|ksi|MPa|disp=table}}
| [[Brinell scale|Brinell]] 183–235
|-
| [[File:Hex cap screw-grade 5.1.svg|75px]] || '''SAE grade 5.1'''<ref name="itp">{{Citation | title = Fastener identification marking | url = http://files.buildsite.com/dbderived-f/industrialthreadedproducts/derived_files/derived331165.pdf | accessdate = 2009-06-23 | postscript =.}}</ref><br />Low or medium carbon steel; quench and tempered || No. 6–{{Frac|1|2}}
| {{convert|85|ksi|MPa|disp=table}}
| colspan=2|
| {{convert|120|ksi|MPa|disp=table}}
| C25–40
|-
| rowspan=2 | [[File:Hex cap screw-grade 5.2.svg|75px]] || '''SAE grade 5.2'''<ref name="itp"/><br />Low carbon martensitic steel; quench and tempered || rowspan=2 | {{Frac|1|4}}–1
| rowspan=2 |85
| rowspan=2 |590
| rowspan=2 colspan=2|
| rowspan=2 |120
| rowspan=2 |830
| C26–36
|-
| '''ASTM A449 - Type 2'''<ref name="itp"/><br />Low carbon martensitic steel; quench and tempered || C25–34
|-
| rowspan=2 | [[File:Hex cap screw-ASTM A325.svg|75px]]or [[File:Hex cap screw-ASTM A325 lines.svg|75px]] || rowspan=2 | '''[[ASTM A325]] - Type 1'''<ref name="fastspec"/><br />Medium carbon steel; quench and tempered || {{Frac|1|2}}–1 (inc.)
| {{convert|85|ksi|MPa|disp=table}}
| {{convert|92|ksi|MPa|disp=table}}<ref name="american"/>
| {{convert|120|ksi|MPa|disp=table}}
| C24–35
|-
| 1–1-{{Frac|1|2}}
| {{convert|74|ksi|MPa|disp=table}}
| {{convert|82|ksi|MPa|disp=table}}<ref name="american"/>
| {{convert|105|ksi|MPa|disp=table}}
| C19–31
|-
| rowspan=2 | [[File:Hex cap screw-ASTM A325 type 3.svg|75px]]<ref name="crnote">Other markings may be used to denote atmospheric corrosion resistant material</ref> || rowspan=2 | '''ASTM A325 - Type 3'''<ref name="fastspec"/><br />Atmospheric corrosion resistant steel; quench and tempered || {{Frac|1|2}}–1
| {{convert|85|ksi|MPa|disp=table}}
| {{convert|92|ksi|MPa|disp=table}}<ref name="american"/>
| {{convert|120|ksi|MPa|disp=table}}
| C24–35
|-
| 1–1-{{Frac|1|2}}
| {{convert|74|ksi|MPa|disp=table}}
| {{convert|82|ksi|MPa|disp=table}}<ref name="american"/>
| {{convert|105|ksi|MPa|disp=table}}
| C19–31
|-
| rowspan=2 | [[File:Hex cap screw-ASTM A354 grade BC.svg|75px]] || rowspan=2 | '''[[ASTM A354]] - Grade BC'''<ref name="fastspec"/><br />Medium carbon alloy steel; quench and tempered || {{Frac|1|4}}–2-{{Frac|1|2}} (inc.)
| {{convert|105|ksi|MPa|disp=table}}
| {{convert|109|ksi|MPa|disp=table}}<ref name="american"/>
| {{convert|125|ksi|MPa|disp=table}}
| C26–36
|-
| 2-{{Frac|1|2}}–4
| {{convert|95|ksi|MPa|disp=table}}
| {{convert|99|ksi|MPa|disp=table}}<ref name="american"/>
| {{convert|115|ksi|MPa|disp=table}}
| C22–33
|-
| [[File:Hex cap screw-grade 7.svg|75px]] || '''SAE grade 7'''<br />Medium carbon alloy steel; quench and tempered || {{Frac|1|4}}–1-{{frac|1|2}}
| {{convert|105|ksi|MPa|disp=table}}
| {{convert|115|ksi|MPa|disp=table}}
| {{convert|133|ksi|MPa|disp=table}}
|
|-
| [[File:Hex cap screw-grade 8.svg|75px]] || '''SAE grade 8'''<br />Medium carbon alloy steel; quench and tempered || {{Frac|1|4}}–1-{{frac|1|2}}
| {{convert|120|ksi|MPa|disp=table}}
| {{convert|130|ksi|MPa|disp=table}}
| {{convert|150|ksi|MPa|disp=table}}
| C32–38<ref name="johndeere"/>
|-
|[[File:Hex cap screw-ASTM A354 grade BD lines.svg|75px]] || rowspan=2 | '''ASTM A354 - Grade BD'''<ref name="Fastenal">{{Citation | title = FastenalTechnicalReferenceGuide | url = http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf | accessdate = 2010-04-30 | postscript =.}}</ref> || {{Frac|1|4}}–2-{{frac|1|2}} (inc.)
| {{convert|120|ksi|MPa|disp=table}}
| {{convert|130|ksi|MPa|disp=table}}<ref name="Fastenal"/> 
| {{convert|150|ksi|MPa|disp=table}}
| C33–39
|-
| [[File:Hex cap screw-ASTM A354 grade BD.svg|75px]] || 2-{{frac|1|2}}–4
| {{convert|105|ksi|MPa|disp=table}}
| {{convert|115|ksi|MPa|disp=table}}<ref name="Fastenal"/>
| {{convert|140|ksi|MPa|disp=table}}
| C31–39
|-
| [[File:Hex cap screw-grade 8.2.svg|75px]] || '''SAE grade 8.2'''<ref name="johndeere"/><br />Medium carbon boron martensitic steel; fully kilned, fine grain, quench and tempered || {{Frac|1|4}}–1
| {{convert|120|ksi|MPa|disp=table}}
| colspan=2|
| {{convert|150|ksi|MPa|disp=table}}
| C33–39
|-
| [[File:Hex cap screw-ASTM A490.svg|75px]]
| '''[[ASTM A490]] - Type 1'''<ref name="fastspec"/><br />Medium carbon alloy steel; quench and tempered
| rowspan=2 | {{Frac|1|2}}–1-{{Frac|1|2}}
| rowspan=2 align=right |120
| rowspan=2 align=right |830
| rowspan=2 align=right |130<ref name="american"/>
| rowspan=2 align=right |900
| rowspan=2 align=right|150 minimum<br/>170 maximum
| rowspan=2 align=right|1,000 minimum<br/>1,200 maximum
| rowspan=2 | C33–38
|-
| [[File:Hex cap screw-ASTM A490 type 3.svg|75px]]<ref name="crnote"/>
| '''ASTM A490 - Type 3'''<ref name="fastspec"/><br />Atmospheric corrosion resistant steel; quench and tempered
|-
| rowspan=3 | || rowspan=3 | '''18-8 Stainless'''<br />Stainless steel with {{nowrap|17–19% chromium and}} {{nowrap|8–13% nickel}}
| {{Frac|1|4}}–{{Frac|5|8}} (inc.)
|rowspan=3 colspan=2|
|align=right|40 minimum <br/>80–90 typical
|align=right|280 minimum <br/>550–620 typical
|align=right|100–125 typical
|align=right|690–860 typical
|rowspan=3|
|-
| {{Frac|5|8}}–1 (inc.)
| rowspan=2 align=right|40 minimum<br/>45–70 typical
| rowspan=2 align=right|280 minimum<br/>310–480 typical
|align=right|100 typical
|align=right|690 typical
|-
| over 1
|align=right| 80–90 typical
|align=right| 550–620 typical
|}
 
=== Metric ===
The international standard for metric screws is defined by [[ISO 898]], specifically ISO 898-1. [[SAE J1199]] and [[ASTM F568M]] are two North American metric standards that closely mimic the ISO standard. In case of inch sizes the grade is dictated by the number of radial shapes plus a value of two. Inch-system bolts use integer values to indicate grades but metric bolts use numbers with one decimal. The two North American standards use the same property class markings as defined by ISO 898.<ref>{{harvnb|Bickford|Nassar|1998|p=154}}.</ref> The ASTM standard only includes the following property classes from the ISO standard: 4.6, 4.8, 5.8, 8.8, 9.8, 10.9, and 12.9; it also includes two extra property classes: 8.8.3 and 10.9.3.<ref name="F568M">{{Citation | title = ASTM F568M - 07 | year = 2007 | url = http://www.astm.org/Standards/F568M.htm | accessdate = 2009-06-06 | postscript =.}}</ref> ASTM property classes are to be stamped on the top of screws and it is preferred that the marking be raised.<ref name="metrichandbook"/>
 
{| class="wikitable collapsible collapsed" width="100%" border="1" style="text-align:center"
! colspan=10 | Head markings and properties for metric hex-head cap screws<ref name="metrichandbook">{{Citation | title = Metric Handbook | url = http://www.blm.gov/nhp/efoia/wo/handbook/h9102.html | accessdate = 2009-06-06 | postscript =. | archiveurl = http://web.archive.org/web/20071031104609/http://www.blm.gov/nhp/efoia/wo/handbook/h9102.html | archivedate = 2007-10-31}}</ref>
|-
!rowspan=2| Head marking
!rowspan=2| Grade, material and condition
!rowspan=2| Nominal size range (mm)
!colspan=2| Proof strength 
!colspan=2| Yield strength, min.
!colspan=2| Tensile strength, min.
!rowspan=2| Core hardness ([[Rockwell scale|Rockwell]])
|-
!MPa!!ksi
!MPa!!ksi
!MPa!!ksi
|-
| [[File:Hex cap screw-class 3.6.svg|75px]]
| '''Class 3.6'''<ref>{{Citation | title = Mechanical properties of bolts, screws, and studs according DIN-ISO 898, part 1 | url = http://mdmetric.com/fastindx/t15u.pdf | accessdate = 2009-06-06 | postscript =.}}</ref>
| 1.6–36
| {{convert|180|MPa|ksi|disp=table}}
| {{convert|190|MPa|ksi|disp=table}}
| {{convert|330|MPa|ksi|disp=table}}
| B52–95
|-
| [[File:Hex cap screw-class 4.6.svg|75px]]
| '''Class 4.6'''<br />Low or medium carbon steel
| 5–100
| {{convert|225|MPa|ksi|disp=table}}
| {{convert|240|MPa|ksi|disp=table}}
| {{convert|400|MPa|ksi|disp=table}}
| B67–95
|-
| [[File:Hex cap screw-class 4.8.svg|75px]]
| '''Class 4.8'''<br />Low or medium carbon steel; fully or partially annealed
| 1.6–16
| {{convert|310|MPa|ksi|disp=table}}
| {{convert|340|MPa|ksi|disp=table}}
| {{convert|420|MPa|ksi|disp=table}}
| B71–95
|-
| [[File:Hex cap screw-class 5.8.svg|75px]]
| '''Class 5.8'''<br />Low or medium carbon steel; cold worked
| 5–24
| {{convert|380|MPa|ksi|disp=table}}
| {{convert|420|MPa|ksi|disp=table}}
| {{convert|520|MPa|ksi|disp=table}}
| B82–95
|-
| rowspan=2 | [[File:Hex cap screw-class 8.8.svg|75px]]
| rowspan=2 | '''Class 8.8'''<ref name="boltdepot"/><br />Medium carbon steel; quench and tempered
| Under 16 (inc.)
| {{convert|580|MPa|ksi|disp=table}}
| {{convert|640|MPa|ksi|disp=table}}
| {{convert|800|MPa|ksi|disp=table}}
|
|-
| rowspan=3 | 17–72
| rowspan=5 align=right |600
| rowspan=5 align=right |87
| rowspan=5 align=right |660
| rowspan=5 align=right |96
| rowspan=5 align=right |830
| rowspan=5 align=right |120
| rowspan=5 | C23–34
|-
| [[File:Hex cap screw-class 8.8 line.svg|75px]]
| '''Class 8.8 low carbon'''<br />Low carbon boron steel; quench and tempered
|-
| [[File:Hex cap screw-class 8.8.3.svg|75px]]
| '''Class 8.8.3'''<ref name="F568M" /><br />Atmospheric corrosion resistant steel; quench and tempered
|-
| [[File:Hex cap screw-ASTM A325M 8S.svg|75px]]
| '''[[ASTM A325M]] - Type 1'''<ref name="uiowa"/><ref name="astm a325m"/><br />Medium carbon steel; quench and tempered
| rowspan=2 | 12–36
|-
| [[File:Hex cap screw-ASTM A325M 8S3.svg|75px]]
| '''ASTM A325M - Type 3'''<ref name="uiowa">{{Citation | title = Metric structural fasteners | url = http://www.icaen.uiowa.edu/~sdesign1/Text/fasteners_si.html | accessdate = 2009-06-06 | postscript =.}}</ref><ref name="astm a325m">{{Citation | title = ASTM A325M - 09 | url = http://www.astm.org/Standards/A325M.htm | accessdate = 2009-06-13 | postscript =.}}</ref><br />Atmospheric corrosion resistant steel; quench and tempered
|-
| [[File:Hex cap screw-class 9.8.svg|75px]]
| '''Class 9.8'''<br />Medium carbon steel; quench and tempered
| rowspan=2 | 1.6–16
| rowspan=2 align=right | 650
| rowspan=2 align=right | 94
| rowspan=2 align=right | 720
| rowspan=2 align=right | 104
| rowspan=2 align=right | 900
| rowspan=2 align=right | 130
| rowspan=2 | C27–36
|-
| [[File:Hex cap screw-class 9.8 line.svg|75px]]
| '''Class 9.8 low carbon'''<br />Low carbon boron steel; quench and tempered
|-
| [[File:Hex cap screw-class 10.9.svg|75px]]
| '''Class 10.9'''<br />Alloy steel; quench and tempered
| rowspan=3 | 5–100
| rowspan=5 align=right |830
| rowspan=5 align=right |120
| rowspan=5 align=right |940
| rowspan=5 align=right |136
| rowspan=5 align=right |1,040
| rowspan=5 align=right |151
| rowspan=5 | C33–39
|-
| [[File:Hex cap screw-class 10.9 line.svg|75px]]
| '''Class 10.9 low carbon'''<br />Low carbon boron steel; quench and tempered
|-
| [[File:Hex cap screw-class 10.9.3.svg|75px]]
| '''Class 10.9.3'''<ref name="F568M"/><br />Atmospheric corrosion resistant steel; quench and tempered
|-
|[[File:Hex cap screw-ASTM A490M 10S.svg|75px]] || '''[[ASTM A490M]] - Type 1'''<ref name="uiowa"/><ref name="astm a490m">{{Citation | title = ASTM A490M - 09 | year = 2009 | url = http://www.astm.org/Standards/A490M.htm | accessdate = 2009-06-06 | postscript =.}}</ref><br />Alloy steel; quench and tempered
| rowspan=2 | 12–36
|-
|[[File:Hex cap screw-ASTM A490M 10S3.svg|75px]]
| '''ASTM A490M - Type 3'''<ref name="uiowa"/><ref name="astm a490m"/><br />Atmospheric corrosion resistant steel; quench and tempered
|-
| [[File:Hex cap screw-class 12.9.svg|75px]]
| '''Class 12.9'''<br />Alloy steel; quench and tempered
| 1.6–100
| {{convert|970|MPa|ksi|disp=table}}
| {{convert|1100|MPa|ksi|disp=table}}
| {{convert|1220|MPa|ksi|disp=table}}
| C38–44
|-
| rowspan=4 | [[File:Hex cap screw-A2.svg|75px]]
| '''A2'''<ref name="boltdepot"/><br />Stainless steel with 17–19% chromium and 8–13% nickel
| up to 20
| colspan=2 rowspan=4 |
| align=right | 210 minimum<br />450 typical
| align=right | 30 minimum<br />65 typical
| align=right | 500 minimum<br />700 typical
| align=right | 73 minimum<br />100 typical
| rowspan=4 |
|-
| '''ISO 3506-1 A2-50'''{{Citation needed|date=June 2009}}<br />304 stainless steel-class 50 (annealed)
| rowspan=3 |
| {{convert|210|MPa|ksi|disp=table}}
| {{convert|500|MPa|ksi|disp=table}}
|-
| '''ISO 3506-1 A2-70'''{{Citation needed|date=June 2009}}<br />304 stainless steel-class 70 (cold worked)
| {{convert|450|MPa|ksi|disp=table}}
| {{convert|700|MPa|ksi|disp=table}}
|-
| '''ISO 3506-1 A2-80'''{{Citation needed|date=June 2009}}<br />304 stainless steel-class 80
| {{convert|600|MPa|ksi|disp=table}}
| {{convert|800|MPa|ksi|disp=table}}
|}
 
==Screw head shapes==
[[File:Screw head types.svg|thumb|400px|right|(a) pan, (b) dome (button), (c) round, (d) truss (mushroom), (e) flat (countersunk), (f) oval (raised head)]]
[[File:Cross slot screw.jpg|thumb|Combination flanged-hex/Phillips-head screw used in computers]]
 
; {{visible anchor|Pan head}}: A low disc with [[chamfer]]ed outer edge
; Button or {{visible anchor|dome head}}: Cylindrical with a rounded top
; {{visible anchor|Round head}}: A dome-shaped head used for decoration.<ref name="mitchell">{{Citation | last = Mitchell | first = George | title = Carpentry and Joinery | page = 205 | publisher = Cengage Learning | year = 1995 | edition = 3rd | url = http://books.google.com/?id=XVFyWYdRsZMC&pg=PA205 | isbn = 978-1-84480-079-7 | postscript =.}}</ref>
; Mushroom or {{visible anchor|Truss head}}: Lower-profile dome designed to prevent tampering
; Countersunk or {{visible anchor|flat head}}: Conical, with flat outer face and tapering inner face allowing it to sink into the material. The ''angle'' of the screw is measured as the [[full angle]] of the cone.
; Oval or {{visible anchor|raised head}}: A decorative screw head with a countersunk bottom and rounded top.<ref name="mitchell"/> Also known as "raised countersunk" (UK)
; {{visible anchor|Bugle head}}: Similar to countersunk, but there is a smooth progression from the shank to the angle of the head, similar to the bell of a [[bugle (instrument)|bugle]]
; {{visible anchor|Cheese head}}: Disc with cylindrical outer edge, height approximately half the head diameter
; {{visible anchor|Fillister head}}: Cylindrical, but with a slightly convex top surface. Height to diameter ratio is larger than cheese head.
; {{visible anchor|Flanged head}}: A flanged head can be any of the above head styles (except the countersunk styles) with the addition of an integrated flange at the base of the head. This eliminates the need for a [[flat washer]].
 
Some varieties of screw are manufactured with a break-away head, which snaps off when adequate torque is applied. This prevents tampering and also provides an easily inspectable joint to guarantee proper assembly. An example of this is the shear bolts used on vehicle [[steering column]]s, to secure the [[ignition switch]].
 
== {{visible anchor|Types of screw drive}}s ==
{{Screws|screw}}
{{Main|List of screw drives}}
 
Modern screws employ a wide variety of drive designs, each requiring a different kind of tool to drive in or extract them. The most common screw drives are the slotted and Phillips in the US; hex, Robertson, and Torx are also common in some applications, and Pozidriv has almost completely replaced Phillips in Europe. Some types of drive are intended for automatic assembly in mass-production of such items as automobiles. More exotic screw drive types may be used in situations where tampering is undesirable, such as in electronic appliances that should not be serviced by the home repair person.
 
==Tools==
[[File:Screw-into-wood.ogg|left|180px|thumb|An electric driver screws a self-tapping phillips head screw into wood]]
 
The hand tool used to drive in most screws is called a ''[[screwdriver]]''. A power tool that does the same job is a ''power screwdriver''; [[power drill]]s may also be used with screw-driving attachments. Where the holding power of the screwed joint is critical, torque-measuring and ''torque-limiting screwdrivers'' are used to ensure sufficient but not excessive force is developed by the screw. The hand tool for driving hex head threaded fasteners is a ''spanner'' (UK usage) or ''wrench'' (US usage).
 
==Thread standards==
{{Sync|Screw thread}}
{{Main|Screw thread}}
 
There are many systems for specifying the dimensions of screws, but in much of the world the [[ISO metric screw thread]] preferred series has displaced the many older systems. Other relatively common systems include the [[British Standard Whitworth]], [[British Association screw threads|BA system (British Association)]], and the [[Unified Thread Standard]].
 
===ISO metric screw thread===
{{Main|ISO metric screw thread}}
 
The basic principles of the ISO metric screw thread are defined in [[international standard]] [[ISO 68-1]] and preferred combinations of diameter and pitch are listed in ISO 261. The smaller subset of diameter and pitch combinations commonly used in screws, nuts and bolts is given in [[ISO 262]]. The most commonly used pitch value for each diameter is the ''coarse pitch''. For some diameters, one or two additional ''fine pitch'' variants are also specified, for special applications such as threads in thin-walled pipes. ISO metric screw threads are designated by the letter '''M''' followed by the major diameter of the thread in millimeters (e.g., ''M8''). If the thread does not use the normal ''coarse pitch'' (e.g., 1.25&nbsp;mm in the case of M8), then the pitch in millimeters is also appended with a [[multiplication sign]] (e.g. "M8×1" if the screw thread has an outer diameter of 8&nbsp;mm and advances by 1&nbsp;mm per 360° rotation).
 
The nominal diameter of a metric screw is the outer diameter of the thread. The tapped hole (or nut) into which the screw fits, has an internal diameter which is the size of the screw minus the pitch of the thread. Thus, an M6 screw, which has a pitch of 1&nbsp;mm, is made by threading a 6&nbsp;mm shank, and the nut or threaded hole is made by tapping threads into a hole of 5&nbsp;mm diameter (6&nbsp;mm - 1&nbsp;mm).
 
Metric [[hexagon]] bolts, screws and nuts are specified, for example, in [[British Standard]] BS&nbsp;4190 (general purpose screws) and BS&nbsp;3692 (precision screws). The following table lists the relationship given in these standards between the thread size and the maximal width across the hexagonal flats (wrench size):
 
{| class=wikitable style="text-align:right"
! ISO metric thread
|M1.6||M2||M2.5||M3||M4||M5||M6||M8||M10||M12||M16||M20||M24||M30||M36||M42||M48||M56||M64
|-
! Wrench size (mm)
|3.2||4.0||5.0||5.5||7.0||8.0||10.0||13.0||17.0||19.0||24.0||30.0||36.0||46.0||55.0||65.0||75.0||85.0||95.0
|}
 
In addition, the following non-preferred intermediate sizes are specified:
 
{| class=wikitable style="text-align:right"
! ISO metric thread
|M7||M14||M18||M22||M27||M33||M39||M45||M52||M60||M68
|-
! Wrench size (mm)
|11||22||27||32||41||50||60||70||80||90||100
|}
 
===Whitworth===
{{Main|British Standard Whitworth}}
 
The first person to create a standard (in about 1841) was the [[England|English]] [[engineer]] Sir [[Joseph Whitworth]]. Whitworth screw sizes are still used, both for repairing old machinery and where a coarser thread than the metric fastener thread is required. Whitworth became ''British Standard Whitworth'', abbreviated to BSW (BS 84:1956) and the ''British Standard Fine'' (BSF) thread was introduced in 1908 because the Whitworth thread was too coarse for some applications. The thread angle was 55°, and the depth and pitch varied with the diameter of the thread (i.e., the bigger the bolt, the coarser the thread). Spanners for Whitworth bolts are marked with the size of the bolt, not the distance across the flats of the screw head.
 
The most common use of a Whitworth pitch nowadays is in all UK [[scaffolding]]. Additionally, the standard photographic [[tripod (photography)|tripod]] thread, which for small cameras is 1/4" Whitworth (20 tpi) and for medium/large format cameras is 3/8" Whitworth (16 tpi). It is also used for microphone stands and their appropriate clips, again in both sizes, along with "thread adapters" to allow the smaller size to attach to items requiring the larger thread. Note that while 1/4" [[Unified National Coarse|UNC]] bolts fit 1/4" BSW camera tripod bushes, [[yield strength]] is reduced by the different thread angles of 60° and 55° respectively.
 
===British Association screw thread===
{{Main|British Association screw threads}}
 
A later standard established in the [[United Kingdom]] was the British Association (BA) screw threads, named after the British Association for Advancement of Science. Screws were described as "2BA", "4BA" etc., the odd numbers being rarely used, except in equipment made prior to the 1970s for telephone exchanges in the UK. This equipment made extensive use of odd-numbered BA screws, in order—it may be suspected—to reduce theft. BA threads are specified by British Standard BS 93:1951 "Specification for British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A."
 
While not related to ISO metric screws, the sizes were actually defined in metric terms, a 0BA thread having a 6&nbsp;mm diameter and 1&nbsp;mm pitch. Other threads in the BA series are related to 0BA in a geometric series with the common factors 0.9 and 1.2. For example, a 4BA thread has pitch <math>\scriptstyle p=0.9^4</math>&nbsp;mm (0.65mm) and diameter <math>\scriptstyle 6p^{1.2}</math>&nbsp;mm (3.62mm). Although 0BA has the same diameter and pitch as ISO M6, the threads have different forms and are not compatible.
 
BA threads are still common in some niche applications. Certain types of fine machinery, such as moving-coil meters and clocks, tend to have BA threads wherever they are manufactured. BA sizes were also used extensively in aircraft, especially those manufactured in the United Kingdom. BA sizing is still used in railway signalling, mainly for the termination of electrical equipment and cabling.
 
BA threads are extensively used in Model Engineering where the smaller hex head sizes make scale fastenings easier to represent. As a result many UK Model Engineering suppliers still carry stocks of BA fasteners up to typically 8BA and 10BA. 5BA is also commonly used as it can be threaded onto 1/8 rod.
 
===Unified Thread Standard===
{{Main|Unified Thread Standard}}
 
The Unified Thread Standard (UTS) is most commonly used in the United States of America, but is also extensively used in [[Canada]] and occasionally in other countries. The size of a UTS screw is described using the following format: '''X-Y''', where '''X''' is the nominal size (the hole or slot size in standard manufacturing practice through which the shaft of the screw can easily be pushed) and '''Y''' is the [[threads per inch]] (TPI). For sizes {{frac|1|4}} inch and larger the size is given as a fraction; for sizes less than this an [[integer]] is used, ranging from 0 to 16.  The integer sizes can be converted to the actual diameter by using the formula 0.060 + 0.013 * number.  For example, a #4 screw is 0.060 + 0.013 * 4 = 0.112&nbsp;inches in diameter.  For most size screws there are multiple TPI available, with the most common being designated a Unified Coarse Thread (UNC or UN) and Unified Fine Thread (UNF or UF).
 
==Manufacture==
[[File:Bolt Forming.svg|thumb|300px]]
[[File:Screw (bolt) 13-n.PNG|thumb]]
{{see also|Threading (manufacturing)}}
 
There are three steps in manufacturing a screw: ''heading'', ''thread rolling'', and ''coating''. Screws are normally made from [[wire]], which is supplied in large coils, or round [[bar stock]] for larger screws. The wire or rod is then cut to the proper length for the type of screw being made; this workpiece is known as a ''blank''. It is then [[heading (metalworking)|cold headed]], which is a [[cold working]] process. Heading produces the ''head'' of the screw. The shape of the die in the machine dictates what features are pressed into the screw head; for example a flat head screw uses a flat die. For more complicated shapes two heading processes are required to get all of the features into the screw head. This production method is used because heading has a very high production rate, and produces virtually no waste material. Slotted head screws require an extra step to cut the slot in the head; this is done on a ''slotting machine''. These machines are essentially stripped down milling machines designed to process as many blanks as possible.
<!--
The process works as follows: the bar stock is fed into a machine, called a "former". The bar stock is stopped, and then gripped by a gripping [[Die (manufacturing)|die]]. The gripping die is shaped in such a way that it forms a carriage along the neck of the stock when its full gripping force is applied. An indented [[Punch (engineering)|punch]], the shape of a rounded head, will then proceed to move forward, colliding with the stock and causing the metal to flow at right angles to the ram force provided by the punch, increasing the diameter of the workpiece, and reducing its overall length, thus forming a "rounded" head. The work billet is then [[Shearing (manufacturing)|shear]]ed to the desired length. ---A ref needs to be found for all this, because the first paragraph states that blanks are made then formed and the second states that the shank and heading occur first then its cut to length. Wizard191-->
 
The blanks are then polished{{Citation needed|date=January 2011}}<!-- It seems more logical that the author meant "clean" and/or "degrease" because polishing is expensive and seemingly unnecessary. --> again prior to threading. The threads are usually produced via [[thread rolling]], however some are [[thread cutting|cut]]. The workpiece is then [[tumble finishing|tumble finished]] with wood and leather media to do final cleaning and polishing.{{Citation needed|date=January 2011}} For most screws, a coating, such as [[electroplating]] with zinc ([[galvanizing]]) or applying [[black oxide]], is applied to prevent corrosion.
 
==History==
[[File:Screw making machine, 1871.png|thumb|right|A [[Lathe (metal)|lathe]] of 1871, equipped with [[leadscrew]] and change gears for single-point screw-cutting.]]
[[File:Brownie-4slide.jpg|thumb|right|A [[Brown & Sharpe]] single-[[Spindle (tool)|spindle]] screw machine.]]
 
While a recent hypothesis attributes the [[Archimedes' screw]] to [[Sennacherib]], King of [[Assyria]], archaeological finds and pictorial evidence only appear in the [[Hellenistic period]] and the standard view holds the device to be a [[Ancient Greece|Greek]] invention, most probably by the 3rd century BC polymath [[Archimedes]] himself.<ref>Stephanie Dalley and [[John Peter Oleson]] (January 2003). "Sennacherib, Archimedes, and the Water Screw: The Context of Invention in the Ancient World", ''Technology and Culture'' '''44''' (1).</ref>{{dubious|date=December 2010}}  Though resembling a screw, this is not a screw in the usual sense of the word.
 
Earlier, the screw had been described by the [[Greek mathematics|Greek mathematician]] [[Archytas of Tarentum]] (428&ndash;350 BC). By the 1st century BC, wooden screws were commonly used throughout the [[Mediterranean]] world in [[screw press]]es for pressing [[olive oil]] from olives and pressing juice from grapes in [[winemaking]]. Metal screws used as fasteners were rare in Europe before the 15th century, if known at all.<ref name="MFA">{{Citation | title = Am_Wood_Screws | url = http://cool.conservation-us.org/coolaic/sg/wag/Am_Wood_Screws.pdf | accessdate = 2010-04-30 | postscript =.}}</ref>
 
Rybczynski has shown<ref name="Rybczynski2000pp34,66,90">{{Harvnb|Rybczynski|2000|pp=34, 66, 90}}.</ref> that handheld [[screwdriver]]s (formerly called "turnscrews" in English, in more direct parallel to their original French name, ''tournevis''<ref name="Rybczynski2000pp32-36,44">{{Harvnb|Rybczynski|2000|pp=32–36, 44}}.</ref>) have existed since medieval times (the 1580s at the latest), although they probably did not become truly widespread until after 1800, once threaded fasteners themselves had become commodified, as detailed below.
 
There were many forms of fastening in use before threaded fasteners became widespread. They tended to involve carpentry and smithing rather than machining, and they involved concepts such as [[dowel]]s and pins, wedging, [[mortise and tenon|mortises and tenons]], [[dovetail joint|dovetails]], [[nail (fastener)|nailing]] (with or without clenching the nail ends), [[forge welding]], and many kinds of binding with cord made of leather or fiber, using many kinds of [[knot]]s. Prior to the mid-19th century, [[Split pin|cotter pins]] or [[clinker (boat building)#Fastening the centre-line structure|pin bolts]], and "clinch bolts" (now called [[Rivet#Types|rivet]]s), were used in shipbuilding. [[Adhesive|Glues]] also existed, although not in the [[profusion]] seen today.
 
The metal screw did not become a common fastener until [[machine tool]]s for their [[mass production]] were developed toward the end of the 18th century. This development blossomed in the 1760s and 1770s<ref name="Rybczynski2000pp75-99">{{Harvnb|Rybczynski|2000|pp=75–99}}.</ref> along two separate paths that soon [[technological convergence|converged]]:<ref name="Rybczynski2000p99">{{Harvnb|Rybczynski|2000|p=99}}.</ref> the mass production of ''wood'' screws [meaning screws made of metal to be used in wood] in a specialized, single-purpose, high-volume-production machine tool; and the low-count, [[toolroom]]-style production of ''machine'' screws (V-thread) with easy selection among various pitches (whatever the machinist happened to need on any given day).
 
The first path was pioneered by brothers Job and William Wyatt of [[Staffordshire]], UK,<ref name="Rybczynski2000p75">{{Harvnb|Rybczynski|2000|p=75}}.</ref> who patented in 1760 a machine that we might today best call a [[Automatic lathe#Screw machine|screw machine]] of an early and prescient sort. It made use of a leadscrew to guide the cutter to produce the desired pitch,<ref name="Rybczynski2000p75"/> and the slot was cut with a rotary file while the main spindle held still (presaging live tools on lathes 250 years later). Not until 1776 did the Wyatt brothers have a wood-screw factory up and running.<ref name="Rybczynski2000p75"/> Their enterprise failed, but new owners soon made it prosper, and in the 1780s they were producing 16,000 screws a day with only 30 employees<ref name="Rybczynski2000p76">{{Harvnb|Rybczynski|2000|p=76}}.</ref>—the kind of industrial productivity and output volume that would later be characteristic of modern industry but was revolutionary at the time.
 
Meanwhile, English instrument maker [[Jesse Ramsden]] (1735–1800) was working on the [[tool and die maker|toolmaking]] and [[:Category:Scientific instrument makers|instrument-making]] end of the screw-cutting problem, and in 1777 he  invented the first satisfactory [[screw-cutting lathe]].<ref name="Rybczynski2000pp97-99">{{Harvnb|Rybczynski|2000|pp=97–99}}.</ref> The British engineer [[Henry Maudslay]] (1771–1831) gained fame by popularizing such lathes with his screw-cutting lathes of 1797 and 1800, containing the trifecta of leadscrew, slide rest, and change-gear gear train, all in the right proportions for industrial machining. In a sense he unified the paths of the Wyatts and Ramsden and did for machine screws what had already been done for wood screws, i.e., significant easing of production spurring [[commodification]]. His firm would remain a leader in machine tools for decades afterward. A misquoting of [[James Nasmyth]] popularized the notion that Maudslay had ''invented'' the slide rest, but this was incorrect; however, his lathes helped to popularize it.
 
These developments of the 1760–1800 era, with the Wyatts and Maudslay being arguably the most important drivers, caused great increase in the use of threaded fasteners. [[Screw thread#History of standardization|Standardization of threadforms]] began almost immediately, but it was not quickly completed; it has been an evolving process ever since. Further improvements to the mass production of screws continued to push [[unit price]]s lower and lower for decades to come, throughout the 19th century.<ref name="Rybczynski2000pp76-78">{{Harvnb|Rybczynski|2000|pp=76–78}}.</ref>
 
The development of the [[turret lathe]] (1840s) and of automatic [[automatic lathe#Screw machine|screw machines]]  derived from it (1870s) drastically reduced the unit cost of threaded fasteners by increasingly automating the machine tool control. This [[demand curve|cost reduction spurred ever greater use]] of screws.
 
Throughout the 19th century, the most commonly used forms of screw head (that is, [[List of screw drives|drive types]]) were simple internal-wrenching straight slots and external-wrenching squares and hexagons. These were easy to [[Machining|machine]] and  served most applications adequately. Rybczynski describes a flurry of patents for alternative drive types in the 1860s through 1890s,<ref name="Rybczynski2000pp79-81">{{Harvnb|Rybczynski|2000|pp=79–81}}.</ref> but explains that these were patented but not manufactured due to the difficulties and expense of doing so at the time. In 1908, Canadian [[P. L. Robertson]] was the first to make the internal-wrenching square socket drive a practical reality by developing just the right design (slight taper angles and overall proportions) to allow the head to be stamped easily but successfully, with the metal [[cold forming]] as desired rather than being sheared or displaced in unwanted ways.<ref name="Rybczynski2000pp79-81"/> Practical manufacture of the internal-wrenching hexagon drive ([[hex key|hex socket]]) shortly followed in 1911.<ref name="US_patent_161390">{{US Patent|161,390}}.</ref><ref name="Hallowell1951pp51-59">{{Harvnb|Hallowell|1951|pp=51–59}}.</ref> In the early 1930s, the Phillips-head screw was invented by [[Henry F. Phillips]].
 
Threadform standardization further improved in the late 1940s, when the ISO metric screw thread and the Unified Thread Standard were defined.
 
Precision screws, for controlling motion rather than fastening, developed around the turn of the 19th century, were one of the central technical advances, along with flat surfaces, that enabled the industrial revolution.<ref name="Rybczynski2000p104">{{Harvnb|Rybczynski|2000|p=104}}.</ref> They are key components of micrometers and lathes.
 
==Other fastening methods==
Alternative fastening methods are:
* [[nail (fastener)|nails]]
* [[rivet]]s
* [[pin]]s (dowel pins, taper pins, roll pins, spring pins, cotter pins)
* [[pinned shafts]] (keyed shafts, woodruff keys, gibb-headed key)
* [[clinker (boat building)#Fastening the centre-line structure]]
* [[welding]]
* [[solder]]ing
* [[brazing]]
* [[Woodworking joints|joinery]] (mortise & tenon, dovetailing, box joints, lap joints)
* [[gluing]]
* [[Adhesive tape|taping]]
* clinch fastening.
 
==See also==
{{div col}}
* [[Gender of connectors and fasteners]]
* [[Tap and die]]
** [[Die head]]
* [[Thread angle]]
* [[Threaded rod]] (e.g., studs, allthread)
* [[Threading (manufacturing)|Threading]]
* [[Thread pitch gauge]]
* [[List of screw drives]]
* [[Syndesmotic screw]]
* [[Dowel]]
{{div col end}}
 
==References==
{{Reflist|2}}
 
===Bibliography===
*{{Citation | last = Bickford | first = John H. | last2 = Nassar | first2 = Sayed | title = Handbook of bolts and bolted joints | publisher = CRC Press | year = 1998 | url = http://books.google.com/?id=NaZwZK2xm-QC | isbn = 978-0-8247-9977-9 | postscript =.}}
*{{Citation
  | last = Colvin
  | first = Fred Herbert
  | last2 = Stanley
  | first2 = Frank Arthur
  | authorlink = Fred H. Colvin
  | title = American Machinists' Handbook and Dictionary of Shop Terms
  | publisher = McGraw-Hill
  | year = 1914
  | edition = 2nd
  | url = http://books.google.com/?id=4Q8LAAAAIAAJ
  | postscript =.}}
* {{Citation | last = Hallowell | first = Howard Thomas, Sr | year = 1951 | title = How a Farm Boy Built a Successful Corporation: An Autobiography | publisher = Standard Pressed Steel Company | location = Jenkintown, Pennsylvania, USA | oclc = 521866 | ref = harv | postscript = . | lccn = 52001275}}
*{{Citation
  | last = Huth
  | first = Mark W.
  | title = Basic Principles for Construction
  | year = 2003
  | publisher = Cengage Learning
  | url = http://books.google.com/?id=BPavrOZxCXAC
  | isbn = 1-4018-3837-5
  | postscript =.}}
*{{Citation | last = Oberg | first = Erik | last2 = Jones | first2 = Franklin D. | last3 = Horton | first3 = Holbrook L. | last4 = Ryffel | first4 = Henry H. | title = Machinery's Handbook | place = New York | publisher = Industrial Press Inc. | year = 2000 | edition = 26th | isbn = 0-8311-2635-3 | postscript =.}}
* {{Rybczynski2000}}
* {{citation
| last = Ryffel
| first = Henry H. (eds)
| title = Machinery's Handbook
| edition = 23rd
| publisher = Industrial Press
| location = New York
| year = 1988
| isbn = 978-0-8311-1200-4
| postscript =.
| author-separator = ,
| display-authors = 1
| author2 = <Please add first missing authors to populate metadata.>}}
*{{Citation | last = Smith | first = Carroll | author-link = Carroll Smith | title = Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook | publisher = MotorBooks/MBI Publishing Company | year = 1990 | url = http://books.google.com/?id=A81HmmRCN7YC | isbn = 0-87938-406-9 | postscript =.}}
 
==External links==
{{Commons category|Screws}}
{{EB9 Poster|Screw}}
* [http://screwsnutsbolts.wix.com/screwsnutsbolts How the World Got Screwed]
* [http://justpaste.it/7ux Screws Small Encyclopedia]
* [http://hdl.handle.net/2060/19900009424 NASA-RP-1228 Fastener Design Manual]  (this link not working)
* [http://www.baconsdozen.co.uk/tools/conversion%20charts.htm Imperial/Metric fastening sizes comparison]
* [http://books.google.com/books?id=2yADAAAAMBAJ&pg=PA149&dq=popular+science+February+1946&hl=en&ei=vOPkTL3jJsnOnAf8toClDQ&sa=X&oi=book_result&ct=result&resnum=5&ved=0CDMQ6AEwBA#v=onepage&q=popular%20science%20February%201946&f=true "Hold Everything", February 1946, ''Popular Science"] article section on screws and screw fastener  technology developed during World War Two
* [http://www.amesweb.info/BoltedJoint/BoltedJointEstimate.aspx Bolted Joint Estimator]
 
{{Woodworking}}
 
[[Category:Metalworking]]
[[Category:Screws| ]]
[[Category:Woodworking]]
 
{{Link GA|es}}

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