Originally Posted by
noglider
I don't know why we got a consensus about pedal threads but not about crank cup threads. Maybe making taps was prohibitively expensive so they wanted to use one tap for both sides. Nah, I wouldn't buy that if you claimed it. Those taps wear out, and if you use a tap half as frequently, it lasts twice as long.
An advantage of using the same thread on both sides of the bottom bracket is that the shell can be threaded on a lathe, simply running the tap through from one side all the way to the other. Dave Tesch told me that was why he liked using Italian thread on his frames.