I have Magnum 91, 4 stroke that I want to put a Tru Turn, or the like, on. The shaft has two prop nuts, the outermost conical and jams the first nut that has a recess for the "cone" of the jam nut. This leaves virtually no thread to mount an adapter. What to do?
Second, how do you figure out how long a a screw is needed?

Thanks all!