Originally Posted by philbob57

There were at least 3 FW threadings: English, Italian, and French. English and Italian are very close. Per wisdom passed down through the ages, it's OK to spin an English FW onto an Italian hub, but it's not OK to go back. French threading is not close enough to either English or Italian to allow mixing.

I expect you'll find very few French-threaded Campy hubs in the US; I mention it because you are likely to find some French-branded, French-threaded hubs on French bikes from the bike boom and earlier.