ah. BB width and threading. most bikes have 68mm wide bb, english threading. there's also italian threading, which means that one of your bb cups will always unscrew itself, and there's french threading, which means you'll never be able to find the part you're looking for (different # of threads-per-inch and whatnot).

my BB, for example (a shimano UN-52 or -53, i forget which. a very solid and reliable and dependable and simple and affordable BB), is measured by saying it's 68 x 107 english threaded.

follow?