- British Association screw threads
British Association or BA screw threads are a largely obsolete set of small
screw threads, the largest being 0BA at 6 mm diameter. They were, and to some extent still are, used for miniature instruments and modelling.
They are unusual in that they were probably the most "scientific" design of screw, with a basis in metric size (the 1mm pitch and 6mm 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 units then in use in the United Kingdom, this was deliberately set to be exact multiples of the metric systemunits, rounded to the nearest thousandth of an inch. This anticipated world-wide metricationby about a century.
British Standards Instituterecommended the use of BA sizes in place of the smaller BSWand BSF screws (those below 1/4"). Generally, the 0BA size was dropped in place of 1/4" 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 1/4" BSF or BSW screw where it was the largest size required.
BA threads are still used in some precision instruments, such as optics and moving-coil meters, relays etc.
BA thread sizes
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 . The major diameter is given by and the spanner jaw size as 1.75 times the major diameter.
The shortening at the crest and root is given by 0.2681683p with a radius of 0.1808346p at both crest and root. The angle of the thread is 47.5 degrees 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 (except 0BA - 6 mm) . 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.
* [http://www.boltscience.com/pages/screw5.htm Bolt Science] writeup.
* [http://www.jag-lovers.org/xk-lovers/library/whitworth_system.html Early history] of non-metric bolts including BA and Whitworth.
* [http://shopswarf.orcon.net.nz/ba.html Table of thread dimensions] .
* [http://www.sizes.com/tools/thread_BA.htm Recommended ISO substitutions] .
* [http://www.baconsdozen.co.uk/tools/spanners.htm#chart Size comparisons Whitworth/BSF/BA/AF and mm]
* [http://www.sat.dundee.ac.uk/~psc/spanner_jaw.html Spanner Jaw Sizes] Additional background information and spanner jaw size table.
Wikimedia Foundation. 2010.
Look at other dictionaries:
British Standard Whitworth — (BSW) is one of a number of imperial unit based screw thread standards which use the same bolt heads and nut hexagonal sizes, some others being British Standard Fine thread (BSF) and British Standard Cycle. These three are collectively called… … Wikipedia
Screw — This article is about the fastener. For other uses, see Screw (disambiguation). Screws come in a variety of shapes and sizes for different purposes. U.S. quarter coin (diameter 24 mm) shown for scale. A screw, or bolt, is a type of fastener… … Wikipedia
Screw thread — Internal and external threads illustrated using a common nut and bolt. The screw and nut pair can be used to convert torque into linear force. As the screw (or bolt) is rotated, the screw moves along its axis through the fixed nut, or the non… … Wikipedia
ISO metric screw thread — The ISO metric screw threads are the world wide most commonly used type of general purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization was set up in… … Wikipedia
Unified Thread Standard — Threads per inch redirects here. For the textile term, see Glossary of textile manufacturing#T. The Unified Thread Standard (UTS) defines a standard thread form and series along with allowances, tolerances, and designations for screw threads… … Wikipedia
Drill and tap size chart — Below is a comprehensive drill and tap size chart for all drills, imperial and metric, and taps up to 36.5 mm. Contents 1 Chart 2 See also 3 References 4 External links … Wikipedia
BA — BABA (or B.A.) may refer to:*Bachelor of Arts *Bangladesh Army *Bank of America *Bell Atlantic now Verizon Communications *The Boeing Company, its stock symbol *British Airways, its IATA airline designator *British Army *British Association for… … Wikipedia
Joseph Whitworth — Infobox Engineer image size = caption = Sir Joseph Whitworth name = Sir Joseph Whitworth nationality = British birth date = December 21 1803 birth place = Stockport death date = January 22 1887 death place = Monte Carlo education = spouse =… … Wikipedia
Ralph Flanders — Infobox Senator name = Ralph Edward Flanders imagesize = 175px birth date = birth date|mf=yes|1880|9|28 birth place = Barnet, Vermont death date = death date and age|mf=yes|1970|2|19|1880|9|28 death place = Springfield, Vermont resting place =… … Wikipedia
History of Greenland — Hunting and whaling have always been important ways to make a living on Greenland. One of the animals found here is the polar bear, which is on the coat of arms of the Danish royal family The history of Greenland is the history of life under… … Wikipedia