I've used a prop nut alone on my saito 100 for months now. Just the prop, washer, and prop nut--no other nut or locking nut. I put a screw driver to it every now and then to make sure it stays tight, but I've never had it loosen up one bit! I know this is contrary to the manual and other folks, but I've done it successfully. In fact, I'm fixing to put the same engine on a Texan, with a dave brown aluminum prop. What I plan on doing with it is using the washer, original nut, and then jamming the adapter up against the nut for locking purposes. I'll check on it every so often to make sure it isn't loosening up. I think one of the biggest keys is how tight you get the first nut on. Get yourself a regular wrench, and don't be afraid to get nasty with it--it has to be tight, especially on four strokes! Then, get that adapter nut tight--real tight, and you should be good to go. This is the setup my brother has right now on his aluminum spinner/saito 100 combo, and is what i'm planning on myself here in a couple of weeks!