The Whitworth thread was the world's first standard [1], devised and specified by Joseph Whitworth in 1841. Until then, every industry had used their own screw threads. The 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 Whitworth thread system was later to be adopted as a British Standard to become British Standard Whitworth.
In the USA, BSW was replaced when steel bolts replaced iron, but was still being used for some aluminium parts as late as the 1960s and 1970s when metric based standards replaced the Imperial ones.
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