Ken Sanford wrote:
they [French bb] are usually for a 68 mm shell --- but measure!!
Campy French and English BB's use the same spindles - but different cups of course. +++++++++++++++++++++++++
Ken is generally right for cotterless, but Sutherland's notes some exceptions. For example, the Shimano D/A BB-7200 spindle apparently is too thick for most other cups.
For cottered cranks, the French and Italian spindles are 16 mm dia, while English spindles are only 15.88 (5/8"). So, you can't run an English crank set with French or Italian spindles; I have successfully done the opposite. similarly, in general, the between-cones centers on British are about 2 mm narrower than on French, which is typically ~2 mm narrower than Italian.
But, during the Civil war, Atlanta was blessed as the terminal for 5 railroads. If I recall the history lesson, none connected, and they used three different guages. It didn't take Sherman to make chaos with moving stuff across town from one line to another. Viva standardization!