RATIO® patented gear technology RATIO® - Calibrated Machine Heads incorporate different string gauges into the tuning equation. From Low E to High E 39:1, 24:1, 20:1, 35:1, 20:1, 12:1. We balanced the gear ratios to each string simplifying the tuning process. With RATIO®, a half-turn is a semi-tone! Every string reacts the same to any tuning adjustment. Predictable, precise tuning, on every string. The PRL-8311, 8322, 8331, 8341, and 8351 are right-handed sets of Locking RATIO® Calibrated Machine Heads for electric guitars that use 3 x 3 tuners, such as Gibson style and PRS style guitars. A great upgrade over single-gear machine heads, such as Grover, Schaller, Sperzel, Kluson, etc. It has a two-pin casing that can be used as is, or with our Patented InvisoMatch Mounting Plates [opens in new tab]. 4 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.