With regard to installing the prop...

First...Tighten the prop to the engine completely using ONLY the Prop Nut.

Second...secure the Prop Nut in place by holding it, then tightening the Lock Nut against the Prop Nut.

When tightening, keep in mind that the intended "target" of the lock nut is... the Prop Nut! Of course the final result will be a secure propeller!

It is a Two Step Process!

I suggest correct sized "combination" wrenches (open end on one end and box end on the other) as opposed to adjustable wrenches for 4 stroke prop installation.