The open backs are a right handed set of open back Ratio Calibrated Machine Heads for Acoustic guitars that use three per side tuners. It has a choice of an intricate skeletonized button or a classic butterbean button.
Ratio - Tuned 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 (give or take) on any string. Every string reacts the same to any tuning adjustment. Predictable, precise and faster tuning and re-tuning.