The Grover Roto-Grip Locking Rotomatics 502 series keystone button tuning machines provide you with a quick and efficient way to keep your instrument in tune. With their sealed-in, lubricated gears and thumbscrew mechanism, you can make precision tuning adjustments and change strings in seconds. The 25/64" post hole and 28.2 mm overall post length give you flexibility in string gauge and let you customize your instrument's tone. For drop-in replacement on a variety of tuners, the 502 series gives you tuning stability you can count on for gigs and studio work.