Klusion TPKB3L-B TonePros 3x3 Locking Tuners - Keystone Buttons - Black This 15:1 gear ratio locking, die-cast 3 + 3 set of tuning machines has a hex-head screw-in bushing (or commonly known as a bolt bushing) The unique string locking feature ensures tuning stability as well as faster string changes by adding a locking mechanism to the top of the string post This requires a 10mm (25/64") peghole for installation and comes with all needed hardware