I have 2 ProSpin aluminum spinners from Mpi, 3" and 3 1/4" respectively. I have experienced bolt failure with both. This usually happens after only 1 to 2 flights, they just break. Same thing happened with the original stock spinner that came with my OS 1.60 FX powered GP Gene Soucy Extra, I suspect it is made by the same people. I don't know if these 4mm bolts are just too weak and need to be replaced with some kind of hardened bolt, but this is driving me nuts. I already lost the original Gene Soucy spinner in flight once and was able to recover the ProSpin replacement that I got for the same plane twice. Now the same thing happened to a brand new 3" spinner I just put on my Seagull Laser 200 (OS 1.20 AX), fortunately this time the plane was still on the ground. I don't think I'm tightening these bolts too much, even though I'm not really sure how tight is too tight. I wonder if anyone out there has had a similar problem.