title_body: How does one hold the motor bell still when tightening prop nuts?
upvoted_answer: You know those rubber wristbands that are given out at lots of events?
  
  You can wrap one of those around the motor bell to get better purchase on it, and then torque down the prop nut.
  
  There are also specialised tools to hold motor bells, such as the one pictured below which can be found here, on Thingiverse.