I read the BSW Wikipedia article. We really take it for granted that a wrench is the size it says it is. I did not appreciate that some wrenches back in the day were instead marked with the diameter of the nut/bolt they were designed to turn.
Also, Whitworth threads to this day are used on Leica camera and enlarger lenses as well as stage lighting equipment mounts (as well as some other stuff). Goes to show you how hard it is to standardize machine tools.