Lose the plastic spinner and your problem will be solved . Plastic just doesn't have enough friction to stop it slipping on either (or both) the prop driver or the prop. There's a work around fix though by using thin leather washers made from old gardening gloves or washers made from "wet and dry" paper that go against the plastic spinner. These just add friction. With a good setup it's surprising how little force is needed to tighten the prop nut enough to stop it coming loose. Even with a 60 or larger I have no problem just using one of those 4 way wrenches.