Also worth bearing in mind that if the propellor is attached to an enginge with a vacuum pump, very often that pump is designed to turn in ONLY one direction. The consequenses of inadvertantly turning the prop in the wrong direction can be a broken vacuum pump and loss of some of the instrumentation.
Whenever inspecting the prop during a pre-flight check, my old instructor used to say "never put more of your hand on the prop than you are prepared to lose...."