Acme Harmoinc Prop Puller.

This puller essentially is a prop nut.  To use it, do the following:

Take off the cotter pin and prop nut.
Thread on the prop puller.  It will not contact the prop.
Strike the prop puller very hard with a large hammer.  The prop should vibrate off the tapered shaft.
Remove prop and key (if not splined).
Replace with new prop and key (if not splined).  Gently tap home.
Thread on prop nut (new if possible, nylock does wear out).
Tighten to spec (typically 30-45 ft lbs, for most men, near full strength with a 10" wrench).
Replace cotter pin, if desired.