Originally Posted by
SkyDog75
Sources I've read seem to indicate that (1) British bottom brackets use BSC threading, and (2) even if that wasn't the case, SAE and BSC thread profiles are compatible. The attached diagram shows CEI (which later became BSC) and American threadforms, and it seems plain to me that a BSC part should thread right into American threads.
If you can cite something that differs, I'd be interested to read it.
Pardon me - I should have mentioned that there are two British threads - the triangular tops and the rounded tops neither of these is strictly compatible with the American flat topped threads. And as I noted they can cause questions among people who aren't expecting the force necessary to put them together the first time.
https://sizes.com/tools/thread_american.htm
But if you've put these together before you'd know that they do not feel compatible the first time together.
Take for instance an XT pedal inserted into a new crank. They thread in the entire way easily by hand. And you need a wrench only to tighten them. This is not the case with mixed English/American threads. Look, I've twisted wrenches on bicycles since the 80's and watched the changes. I still think of the Peugeot PX-10 as one of the best handling bikes I've ridden. But you couldn't use one now because of the French threaded bottom brackets. So if you're a steel man you go with a Basso Loto.