Graph Tech Ratio 6-in-line electric guitar locking tuners deliver predictable, precise tuning on every string. Graph Tech balanced the gear ratios to each string to simplify the tuning process. With Ratio 6-in-line tuning machines, a half turn is a semi-tone. The Graph Tech PRL-8721 is a right-handed set of locking Ratio calibrated machine heads for electric guitars that use 6-in-line tuners. It has a two-pin casing that can be used as is, or with Graph Tech’s patented InvisoMatch mounting plates. Four different sets of InvisoMatch mounting plates in brushed aluminum are included to make installation on most guitars fast and accurate by using your existing screw mounting holes.