Grover Rotomatic 406G mini locking guitar tuning machine heads make quick work of tuning. With a gear ratio of 18:1, these locking tuners give you all the benefits of standard Rotomatics - plus the positive locking of Grover's internal cam post. Insert your string through the string hole, pull to tension by hand, and start to tune. As you begin tuning, only the locking cam in the string post turns. The string post begins to turn once the string is locked. In under one string post revolution, you'll be in tune. And you'll stay in tune, with Grover's Rotomatic 406G locking guitar tuning machines. Grover: exceptional quality and lifetime warranty Grover has been keeping the world's finest stringed instruments in tune for over a century. Grover started out in the late 1800's producing banjo and guitar tuning machine heads. Eventually the company expanded into making tuners for mandolin, dulcimer, ukulele,