The Whitworth BSW – the world’s first national screw thread standard, devised and specified by Joseph Whitworth in 1841. Until then, the only standardization was what little had been done by individual people and companies. Some of the companies’ in-house standards spreading a bit within their industries. Whitworth’s new standard specified a 55° thread angle and a thread depth of 0.640327p and a radius of 0.137329p, where p is the pitch. The thread pitch increases with diameter in steps specified on a chart.
The form of the thread is based on a fundamental triangle with an angle of 55° at each peak and valley. The sides are at a flank angle of Θ = 27.5° perpendicular to the axis. Also later, The British Standard adopts the Whitworth thread system to become British Standard Whitworth.
British Standard Threads Whitworth BSW