I've got two of these fans, and they're the best I've ever had in the 64 mm class. What I like most about these fans is the way they adapt to the shaft of the motor (3mm shaft). They essentially use a prop adaptor, which is very easy to access with a flat screwdriver right from the front. No more hassling with small hexnuts at the base of the adaptor. However, make sure you tighten really well, because once I tested static trust with an oversized battery and the fan came off... I have not tested this myself, but you may be able to get a bigger inner-diameter adaptor from headsuprcDOTcom to mount the fan on a 3.17 mm or 4mm motor HYPOTHETICALLY. Both fans came perfectly balanced. Coincidence, perhaps, but I won't complain. The only tiny minus I have is that this is a 5 blade fan, and a faster higher revving motor doesn't get you beyond a certain max trust. I had one motor in the fan once that was too strong and the fan blades made this howling noise that you also get with thin slow fly props on oversized motors, most likely because of the blades twisting. No biggy though. So, all in all, highly recommended.