Information on Screw Threads

British Standard Whitworth Thread

Sir Joseph Whitworth proposed this thread in 1841. This was the first standardised thread form. The form of the thread is shown in the diagram. The principal features of the British Standard Whitworth (BSW) thread form are that the angle between the thread flanks is 55 degrees and the thread has radii at both the roots and the crests of the thread. The relevant standard for this thread form is the British Standard BS 84 - 2007. The thread form is now redundant and has been replaced by Unified and Metric threads but there are many applications in which it is still used. The British Standard Fine (BSF) thread has the same profile as the BSW thread form but was used when a finer pitch was required for a given diameter.


p = pitch of the thread

d = depth of the thread

r = radius at the top and bottom of the threads


d = 0.640327 p

r = 0.137329 p

British Standard Brass (BSB) Threads

There are other threads that are based upon the Whitworth thread form. British Standard Brass (for which there is no British Standard) is based upon the Whitworth thread form with all diameters having 26 threads per inch (tpi). It was used on general brass work, gas fittings and brass tubing. It is also reported that antenna bases should use this thread. The specific dimensions for the thread can be derived by treating it as a special Whitworth thread. The thread may have come about as an attempt at standardisation by gas burner fitting manufacturers.

Model Engineers (ME) Threads

Established in 1912, the Model Engineers thread is based upon the Whitworth thread form and was used in instrumentation as well as by model makers. It was a fine pitch thread having 32, 40 or 60 (tpi).

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