Propellers by Quanum from HobbyKing have very unpractical holes. I got a few of them for my test but they did not fit my motors. I wanted to use the propellers with Dualsky 5015 and/or Dualsky 7010 motors. I had to modify the propellers mount holes. That was not easy as the middle hole is 8mm and the four mounting holes overlap 15x15 7010 motor holes. To solve that I cut special elements that partly go into the holes. After gluing two of such elements I was able to cnc cut holes wherever I wanted.