[Deke]

Hex shaft is one thing that is impractical for normal engineering designs. It creates stress concentrations within the inner bearing race with 6 sharp corners, and it must be designed with a slip fit. That slip fit is slowing wearing over time, but it does fine for a few hundred hours of FRC time. It is a slick way to not deal with key locks.

Along those same lines, you can get away with slip fits and some loc tite in axles/bearings, where you would normally press fit details. That is what took me a while to understand, because you don't need the thousands of hours of reliability.