And as a further digression, there's the multitude of different standards for bicycle bottom bracket threads from Raleigh, English, French, Italian....
I have a Volvo 300 outside which is mainly metric, but the cheeky so-and-sos used Imperial front hub nuts. I used to have a Reliant Kitten which was Imperial threaded in the brake department, with the exception of the compensator valve which was Metric threaded. Although physically the same shape and bore size, from past experience Austin Maxi rear brake wheel cylinders are Imperial and Austin Allegro ones are Metric.