Re: the thickness of screw threads was not fully standardized in the US
Having an interest in vintage vehicles, I seem to have developed rather more knowledge of thread systems than I really wanted to. So my early 1950s British motorcycle uses all of the following:
Whitworth (British Standard Whitworth - BSW) - Developed by Sir Joseph Whitworth and modestly named after himself. The hexagonal heads and nuts were quite chunky and in the early 20th Century nuts and bolts were being made with the next size smaller head.
British Standard Fine (BSF) - Developed in early 20th Century with a finer pitch than Whitworth and using the one size smaller head, but otherwise the same.
British Association (BA) - A metric system that starts at 6mm OD and 1mm pitch and then goes down in a geometric progression (as the BA number increases). Whilst the smallest used is typically around 16BA, you can calculate the dimensions of 20BA or even 100BA. When adopted by the British all the dimensions were specified in inches!
Cycle Thread - Mostly 26TPI regardless of size.
British Standard Pipe (BSP) - I suspect we've managed to inflict this on the rest of the world and almost the opposite of BA it's now specified in millimetres.
Although the British have now moved to the metric system there are still gotchas, such as the Japanese using a slightly different (finer) thread for some sizes!
As you can probably tell, I'm an absolute blast at parties (if I were ever to be invited to one)!