..........maybe this is just me, but from what i always thought, (i dont know about other types of cars but mine is like this) that the allen wrench hole in the middle of the bolt was to put a allen wrench in while u took a normal open end wrench and turned the nut and held the allen wrech so the center wouldnt spin. i got it preetttttyyy tight doing that cause the allen key thing was long enough to hit the body pf the car and held itself. but sometimes when im pulling up something at a angle i hear a loud noise like its still loose, but im not sure. does that means it needs to be even tighter?