BSW stands for British Standard Whitworth, which is a thread standard that originated in the UK and is named after its creator, Sir Joseph Whitworth. First introduced in the 1840s, it was the world’s first national screw thread standard designed for engineering and manufacturing purposes.

The Whitworth thread form is characterized by its distinctive 55-degree thread angle and rounded peaks and valleys, which is different from other thread standards such as the Unified Thread Standard (UTS) that typically have a 60-degree thread angle. The rounded profile of the Whitworth threads helps distribute stress evenly, which was especially beneficial for the manufacturing processes.