The Graph Tech Ratio 2+2 Bass Y-Style Button machine heads deliver predictable, precise tuning, on every string. Each string reacts the same to any tuning adjustment. Graph Tech has balanced the gear ratios to each string, which simplifies the tuning process. With Ratio tuners, a half turn is a semi-tone. The Graph Tech PRB-4220 is a right-handed set of Ratio calibrated machine heads for bass guitars that use a 2 x 2 configuration. To achieve the higher gear ratios, Ratio tuners use a double envelope gear design with a hardened steel gear.