Originally Posted by
verktyg
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.
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.
Also been there. In 1964, I installed a BSA sprocket on my new Helyett Speciale track bike, which was built with all French parts. Wasn't long before the sprocket broke loose under load.
The mechanic at the bike shop took off the sprocket and wrapped the the threaded portion of the hub in aluminum foil. That quick-and-dirty repair held up for the next couple of years, until I sold the bike to a fellow who used to post on here using the name Stronglight. That was the beginning of his fascination with French bikes.