[R.C.]

Depending on the situation and motor:

For cims we use these:

McMaster: 94800A730

For other various applications we avoid keys for multiple reasons:

-You lose them easily
-A pain to put in and take out
-Would rather use HEX shafting.

If you are left with a key:

-Use PushNuts (Linked Above)
-Clamp Collars work great if you have clearance.
-Snap rings work great (Need a lathe of some sort)

-RC