We got into a discussion of all the metalworking and related standards: a mile is 1000 Roman Soldier paces, standard train track gage is from the Roman chariots. The various sheet metal and wire gages are mostly based on weight per square foot of the number of sheets. Letter drill sizes are just the odd sizes needed in between fractional sizes. shotgun gage is number of round lead balls per pound. Pipe sizes are the minimum inside diameter of standard pipe wall thickness.
But where do the screw sizes from 0 to 14 come from? #12 is pretty much3/16" but the others????