There are two major types of one-piece crank sets, differentiated by their axle threading. The more common size uses 24 threads per inch, but some bikes, particularly older U.S. made Schwinn and Mongoose models, use 28 threads per inch.

No part of the bearing assembly is interchangeable between threadings.


24 TPI cranks use #66 retainers, with 10 5/16" balls.

28 TPI cranks use #64 retainers, with 9 5/16" balls.


The pressed-in cups are also a slightly different size internally, though they both fit the same frame bottom brackets. It is usually a good idea to buy a whole set (cones, cups, retainers) if there is serious wear to any of the parts. These are not expensive. Good sets are less than $20.