Basil,

I believe the standard nut and lock-nut must be used, to prevent the prop from ever being thrown, in an event of a back-fire. Most four-strokes will have a long enough shaft thread, to also allow the spinner nut.

After tightening the standard prop nuts securely, the spinner nut does not have to be tightened very strongly, since it is merely used as a go-between, for the spinner cone bolt to thread into.

But don't just loosely fit it. Tighten, but do not "gorilla" it, on the shaft's remaining threads.

So yes, you may have three nuts on the shaft.