This may be old news but I learned to watch out for collet type prop adapters. I was using a Eflite 400 920 Kv motor with a 10/6 prop on three cells and wanted to run up the motor for testing. The Eflite collet prop adapter was as snug against the prop as possible and when I turned the motor on-gradually to full power- the prop flew off of the model and thank God just missed me. I did not think a 400 motor would be too much for the collet to safely restrain the prop from flying off! When I tried a set screw Eflite prop adapter I striped the threads with just a little force from my Allen wrench but thank God the shaft was flat ground and held the prop more safely when I tried another prop adapter. Has any one had the same problem? I'll go with set screw adapters from now on but even though the adapters have two threaded securing holes they only provide one grub screw!