Original Grover Locking Rotomatics - Sold as a set of 6, 3 aside. Includes washers, wood screws and bushings. 18:1 gear ratio. Simply insert the string through the hole, pull to tension by hand and begin tuning. As you tune, only the locking cam in the post turns. Once the string begins to turn, it can be tuned to pitch. In less than one revolution of the post, you will be in tune and locked. Gear box has a special lubricant for lifetime, trouble free service. Will directly fit onto a PRS SE.