Schaller BM Bass Machine Heads Model: 4 left Wings: BM Shaft length: Solid Headstock 20.3mm Ratio: 1: 20 Including: 4 press-fit sleeves, 16 mounting screws Finsih: Black Chrome Classic look with the big wing (1mm less wide than in BMF) and with a compact base plate for easy installation even on smaller head plates. Precisely manufactured for maximum ease of use, comfortable tuning and high tuning stability. Incidentally, this mechanism can be done in a few simple steps be mounted from left to right (and vice versa).