[jman4747]

Originally Posted by Cory

The obsession with hex is because round keyed stock is completely inferior in every way (except perhaps availability).

Strength (massive stress risers)
Ease of use...no keys to lose during installation. No struggling to get the key in/out of the keyway on either mating part. No need to cut keys.
Torque transmission (which goes into strength)
The list goes on and on.

Well outside of FRC and just so students who might be mechanical engineers one day know, round shaft has its perks.

1. Round shaft is available in any material that can be put on a lathe

2. Round shaft, depending on how it's machined, will hold tighter tolerances than hex shaft which can be unbelievably important in various real world applications

3. Machining internal features for round shaft is (depending on the tolerances required) easier, faster, more precise, and cheaper than for hex

Round shaft is not "completely inferior in every way" to hex. Hex shaft is easier to use and commonly meets the needs of most FRC applications but when your're in the real world there are times when you may need something else.