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| '''British Association''' or '''BA''' screw threads are a largely obsolete set of small [[screw thread]]s, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling.<!--UK spelling on a British thread-->
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| They are unusual in that they were probably the most "scientific" design of screw, with a basis in metric size (the 1 mm pitch and 6 mm diameter of 0BA) and with a mathematical relationship between the 'number' (e.g. 2BA with K=2) and the corresponding pitch, major diameter, and then spanner size. Though originally defined in terms of the [[imperial unit]]s then in use in the United Kingdom, this was deliberately set to be exact multiples of the [[metric system]] units, rounded to the nearest [[Thou (unit of length)|thousandth of an inch]]. This anticipated worldwide [[metrication]] by about a century. The design was first formulated in 1884, following a study of Swiss practice and was standardised in 1903.
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| The [[British Standards Institution]] recommends the use of BA sizes in place of the smaller [[British Standard Whitworth|BSW]] and [[British standard fine thread|BSF]] screws (those below 1/4").<ref name="bs93:2008"/>{{rp|4}} Generally, the 0BA size was dropped in place of 7/32" BSF in assemblies that included larger fasteners, however, in smaller equipment that was primarily electronic/electrical the 0BA size would typically be used in place of the BSF or BSW screw where it was the largest size required.
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| BA threads are still used in some precision instruments, such as optics and moving-coil meters, relays etc. A 2BA thread is used to connect the head of a [[Darts|dart]] to its shaft — as such, it is one of the few common uses of this thread in North America.
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| 2BA threads are commonly found in the old imperial [[British Engineering Standards Association|BESA]] conduit boxes in the UK which are still in use (but not installed) today.
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| ==BA thread sizes==
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| The pitch of 0BA is 1 mm and the pitch of each higher numbered thread is obtained by multiplying the pitch of the lower number by 0.9 so K-BA has a pitch of <math>\scriptstyle p=0.9^K</math><ref name="bs93:2008">{{cite book|author=British Standards Institution|title=British Association (B.A.) screw threads – requirements|isbn=978-0-580-60893-3|id=BS 93:2008}}</ref>{{rp|12}}. The major diameter is given by <math>\scriptstyle 6p^{1.2}</math><ref name="bs93:2008"/>{{rp|12}} and the hex head size (across the flats) is 1.75 times the major diameter.
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| BA sizes are specified by the following [[British Standards]]:
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| *BS 93:1951 — Specification for British Association (B.A.) screw threads with tolerances for sizes 0 B.A. to 16 B.A.
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| *BS 93:2008 — British Association (B.A.) screw threads. Requirements
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| The shortening at the crest and root is given by 0.26817''p'' with a radius of 0.18083''p'' at both crest and root.<ref name="bs93:2008"/>{{rp|2}} The angle of the thread is 47.5 degrees<ref name="bs93:2008"/>{{rp|2}} which is different from that used by Whitworth (55 degrees) and ISO Metric (60 degrees) so BA fasteners are never interchangeable with Whitworth/Metric ones even when the pitch and diameter seem similar (e.g. 0BA which appears similar to M6x1mm). Standard BA sizes are defined between 0BA and 22BA. The very small sizes are not used very often and other standards tend to be used (e.g., NHS).
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| <CENTER>
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| {| class="wikitable"
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| |-
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| ! BA
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| ! Outer<br />Diameter<ref name="bs93:2008"/>{{rp|7, 16}}
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| ! Threads<br />per inch
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| ! Threads<br />per mm
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| ! Tap drill
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| |-
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| | 0
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| | 0.2362 in / 6.0 mm
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| | 25.38
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| | 1
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| | 5.1 mm / 7 gauge
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| |-
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| | 1
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| | 0.2087 in / 5.3 mm
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| | 28.25
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| | 1.112
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| | 4.5 mm / 16 gauge
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| |-
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| | 2
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| | 0.1850 in / 4.7 mm
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| | 31.35
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| | 1.234
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| | 4.0 mm / 21 gauge
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| |-
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| | 3
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| | 0.1614 in / 4.1 mm
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| | 34.84
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| | 1.372
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| | 3.4 mm
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| |-
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| | 4
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| | 0.1417 in / 3.6 mm
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| | 38.46
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| | 1.514
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| | 3.0 mm
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| |-
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| | 5
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| | 0.1260 in / 3.2 mm
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| | 43.10
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| | 1.697
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| | 2.65 mm / 37 gauge
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| |-
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| | 6
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| | 0.1102 in / 2.8 mm
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| | 47.85
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| | 1.884
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| | 2.3 mm
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| |-
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| | 7
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| | 0.0984 in / 2.5 mm
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| | 52.91
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| | 2.083
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| | 2.05 mm / 46 gauge
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| |-
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| | 8
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| | 0.0866 in / 2.2 mm
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| | 59.17
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| | 2.330
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| | 1.8 mm
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| |-
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| | 9
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| | 0.0748 in / 1.9 mm
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| | 64.94
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| | 2.557
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| | 1.55 mm
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| |-
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| | 10
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| | 0.0669 in / 1.7 mm
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| | 72.46
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| | 2.853
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| | 1.4 mm / 54 gauge
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| |-
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| | 11
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| | 0.0591 in / 1.5 mm
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| | 81.97
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| | 3.227
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| | 1.2 mm
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| |-
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| | 12
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| | 0.0512 in / 1.3 mm
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| | 90.91
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| | 3.579
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| | 1.05 mm
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| |-
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| |}
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| </CENTER>
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| ==Notes==
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| {{reflist}}
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| ==External links==
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| * [http://www.boltscience.com/pages/screw5.htm Bolt Science] writeup.
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| * [http://www.baconsdozen.co.uk/tools/conversion%20charts.htm] Comparison chart of Whitworth/BSF,AF metric and BA spanner sizes.
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| * [http://www.jag-lovers.org/xk-lovers/library/whitworth_system.html Early history] of non-metric bolts including BA and Whitworth.
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| * [http://shopswarf.orcon.net.nz/ba.html Table of thread dimensions]
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| * [http://www.sizes.com/tools/thread_BA.htm Recommended ISO substitutions]
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| * [http://www.sizes.com/library/technology/thread_BA1.htm First] and [http://www.sizes.com/library/technology/thread_BA2.htm second] report of the BA Small Screws Committee
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| * [http://www.britishfasteners.com/threads/ Useful comparison of obsolete British threads]
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| [[Category:Mechanical standards]]
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| [[Category:Screws]]
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| [[Category:Threading (manufacturing)]]
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| [[Category:British standards]]
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The author is recognized by the title of Figures Lint. South Dakota is exactly where me and my spouse live and my family members loves it. Doing ceramics is what her family members and her appreciate. Hiring is her working day job now but she's always wanted her personal business.
Here is my web-site - home std test