Marine engineering is where British Standard threads really asserted themselves or, more precisely, were mandated by the British Admiralty. British Standard Whitworth, which is mostly known simply as “whitworth” today was the first standardised thread, from the middle of the 19th century. There is a story in the text books which goes some way to explaining British Naval superiority through the efficiency of production techniques achievable through standardisation.
British standard fine was a later development for precision applications in steel. The thread profile allows parts to be placed under higher torque prior to failure. From memory BSF is still at the same pitch as Whitworth but has less depth of cut (and is obviously finer).
Whitworth was developed prior to steel being readily available, inexpensively at consistent quality so it’s coarser pitch and form reflect the tooling, materials and applications of that time.
I have a set of taps and dies for Whitworth that predates me by three generations, they are in a very well made Cedar box. The quality of the parts is amazing and the grandfather who passed them down to me explained that they were extremely expensive. I was told that they came from his father and were used to repair the steam engines that powered their sawmill. I have used them to repair threads on vintage machines, they’re a little more fiddly to set up than more modern dies but work just fine despite being around a century old.
