Grover Roto-Grip Locking Rotomatics 502 series standard button tuning machines provide you quick and easy tuning for your instrument. With their famous Rotomatic design and thumbscrew mechanism, you can lock strings into place in seconds. The sealed-in, lubricated 18:1 gear ratio gives you precision tuning for stable intonation. The 502 series drops into many industry-standard tuners, letting you upgrade your instrument with pro-level performance.