RE: Spinner came off when starting oops, why?
You must tighten the prop nut really tight. If the prop is plastic, tighten the nut with a 4 to 6 inch wrench as tight as you can. If the prop is wood, slightly less torque, because you can crush the wood prop.
The normal direction of the starter is trying to remove the prop, so it must be really tight to resist this.