What are you tightening it with? I use an allen wrench or a screw driver that fits the hole in the nut. On the .15s I sometimes bend the screwdriver to get it tight enough, if I'm not careful. There is probably a hardened piece of something that would make the perfect nut wrench, but I haven't found it yet, maybe music wire. Sometimes I cut my fingers on the prop if I haven't scraped the flashing off well enough. That's how tight I am twisting mine down. I wouldn't use Loc-tite, you might not get it back apart after you shear both prop blades off.

rrh