Since I had planned to tighten the tuning machines on my new Fender MIM standard jazz bass, I thought I might as well take a few pictures and post a little tutorial: If the tuning machines on your MIM bass feel loose and unprecise, the following tip will tighten them: First remove the strings from the headstock: A look at the back of the headstock. Get out your screwdriver and unscrew the large philips screw on top of the gear, and you'll be able to disassemble it: Let the tuning post drop away. Underneath the wheel you'll find two washers, a black plastic washer and a metal one. Their job is to make sure the gear's wheel and worm fit tightly together: Here they are, removed from the whorm-wheel: The metal washer has a slight bend to it. The more it is bent, the tighter the gear of the tuning machine will work. Now carefully bent the metal washer, so it is slightly concave: Now you just need to re-assemble the whole enchilada, and voila, your tuning machine will be nice and tight! If it is too tight now, you simply have to unbend the metal washer a bit. Remember this tip is for Mexican Standards only. AFAIK, the other Fender basses use another system.