Originally Posted by Gluehand
1. The spline top Ø is the same as the rear of the shaft (5 mm), i.e. the propriver will stop (kind of) at the rear end of the groove, but further tightening of the prop nut, would chew the alu splines off at the propdriver inner...luckily no one has done this (the crankcase stops the movement before this happens)
2. The propdriver is splined right thru, i.e. the shoulder does not provide a stop.
Well, if it were mine, I'd be tempted to get some soft-ish wire and form it such that it fits into that groove, thus preventing the prop driver from moving back along the crankshaft. Seizing wire or even copper wire should do the trick. As you suggest, the prop driver will prevent the wire from "popping out" of the groove.