Machine heads without a sealed gear are criticized for not having the same smooth performance, efficiency and durability that sealed gear tuners have. The SD series solves these problems by combining "Rock-solid" technology and the post collar or: "Self-Center Guide", found on enclosed gears in the base plate of the gear allowing the post to perfectly align itself with the bushing which attaches the gear to the headstock. The SD series uses a torque balancer to ensure steady rotation of the tuner button giving high quality sound performance as well as great functionality.