I have flat spots on some motors and on others I do not. With the 4mm set screw, I don't think it makes a difference, as Mike said. If you don't have the tap and bit, dubro sells them as a set pretty cheap.

The 1515/1Y is one nice motor. I think I'm gonna grab one. I just want to wait and see how my 7XL runs with the Compro I have coming in first.