Kurt Sperry asked:
<< > Has anyone ever had a French fixed cup loosen on them? I've had several
French threaded bikes and I haven't ever seen any evidence of that. I
suspect RH fixed cup threads are just fine in the real world.>>
The vast majority of REALLY difficult fixed bottom bracket cups I have had to remove in the past 30+ years were French threaded.
Cheers,
Chuck Brooks
Malta, NY