The Grover Professional mandolin F Style (409 Series) open-gear tuning machines provide precision tuning for serious mandolin players. Their specially engineered worm gears and die-cast plates keep the tuning posts perfectly aligned so you can achieve note-perfect intonation. The 18:1 gear ratio gives you fine control over the tuning, while the bell-shaped pearl buttons add vintage styling. The 25/64" post holes and included mounting hardware make installing these tuners on your mandolin a straightforward process. Once in place, their smooth operation and rock-solid construction will have you tuning with confidence at every gig or studio session.