Upgrade any model with a six-in-line headstock with this full pack of Graph Tech PRN-2731 Ratio Electric machine heads, and you're not only reinforcing the tuning stability, but simplifying and refining the entire tuning process. Each machine head is numbered to match the corresponding string and mounting position since the ratio has been finely tuned per head to ensure that you can make the same adjustment to result in the same pitch alteration. For example: by turning any tuning button by a whole rotation, the pitch is taken up or down by a whole note. A highly innovative setup that supports highly intuitive tuning. To finish, a set of InvisoMatch standard mounting plates comes included so the PRN-2731 Ratio Electric machine heads will be compatible with the headstock of virtually any six-in-line model without having to modify the ferrule or screw holes.