I think we are talking about 2 different issues. One is the collet slipping on the shaft, the other is the prop slipping on the collet. I had the first issue with a Badass motor on a 5mm shaft. One of my flying buddies, Ken Cook, told me to spray the shaft with some accelerator or wipe it with alcohol. I thought that was a little crazy but he has never steered me wrong. I tried it and it work instantly, the collet grabbed on to the shaft with no slippage.