This question has been brought up to team drivers before. The set screw is not neccesary. I have run my ball diff in my impulse for two years EVERY WEEK without the setscrew and NEVER had a problem. Just simply use loctite on the adjustment screw. Then, the thrust bearings are what keep the diff from loosening or thightening. The set screw is somewhat of a (unneccesary) fail-safe.