Home Featured Grover Announces Roto-Grip Locking Super Rotomatic Tuners Grover Announces Roto-Grip Locking Super Rotomatic Tuners planetsixstring March 3, 2021 comments off Tweet on Twitter Share on Facebook Google+ Pinterest This post was originally published on this site These locking machine heads use a 3-step button, 18:1 Rotomatic design, and a “thumb screw” mechanism.