The PRN-3411 is a right-handed set of open back RATIO® Calibrated Machine Heads for acoustic guitars that use 3+3 side tuners. It has an intricate skeletonized button and finish selection. 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, 14:1, 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.