Originally Posted by
Andy_K
Are you sure you don't have that backward? I'm experiencing the opposite, I think. French threaded freewheels will start to thread onto non-French threaded hubs, but will bind after a few turns.
No, British freewheel threads are .004" - .002" per side larger, ISO threads are .009" larger - .0045" per side and Italian freewheels are .012" larger, .006" per side so they will fit over the outside diameter of a French threaded hub.
The problem is the difference in the thread pitches. At 5 turns there's a .0115" or 0.295mm pitch error. See graphic below.
Aluminum threads on hubs are soft. Forcing a British, ISO or Italian freewheel on a French hub will deform the threads, weakening them. You are essentially re-threading the hub producing very weak threads.
A 1mm pitch thread has a theoretical height of ~ .046mm (.025" for 24TPI). You will mush off the top 1/3 to 1/2 of the threads by forcing a 24 TPI freewheel onto to a 1mm thread pitch hub. There's not much material left.
If you put enough force into the weakened threads like honking up a hill, you can easily spin the FW destroying the remaining threads and trashing the hub, especially with Italian on French.
Been there, done that. Means not being able to pedal home. Someone else did the misfit not me.