The PRL-8341 is a left-handed set of Locking RATIO® Calibrated Machine Heads for electric guitar that use 3 x 3 tuners, such as Gibson style and PRS style guitars. A great upgrade over a single gear machine heads, such as Grover, Schaller, Sperzel, Kluson, etc. Probably the easiest machine heads to retrofit using the Invisomatch Mounting Plates which allows you to use your existing screw holes. 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. 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.