title_body: How to keep my prop from flying off my motor?
upvoted_answer: It looks like you are missing a piece of the prop adapter.
  There should be three pieces, the nut, the central shaft with a thread for the nut on one end and a taper on the other, and a collar that matches the taper. You're missing the collar.
  The nut forces the collar onto the taper, which squeezes the slots together, gripping the shaft. They're normally very secure but won't work without all three parts.
  Here's a picture (I get an error when I try to embed it) or you could just look for pictures of 'collet prop adapter'.
  https://shop.pichler.de/Collet-Cone-Prop-Adapter-60mm