If you mean the little ones on the saddles, you may have to go to a music store to find one. They are really small so a standard size set of hex wrenches may not have one small enough to fit.
A general rule of thumb. If it was made in the USA it will be SAE or "imperial" referring to inches, if it was made in Asia or Europe it will be metric. There are of course exceptions to every rule but that one is a good start.