Well,I'm a pretty big boy, and I could tighten the nut till I snap the shaft clean off!I Know it's a hands on kind of thing, but I think I'm going as tight as anyone would dare.All the props are Master Airscrew plastic in various sizes,and I've tried T/F Powerpoint wood.Some spinners come with sandpaper type discs...tried em'...comes loose!Looks to me like the spinner backplate could be a weak point, so I take the spinner assy. off completely for a good bite into the engines' toothed plate.Guess what...comes loose! I Dunno,maybe it's my curse?