6N137 high-speed OptoCouple to ensure high speed without losing steps • for 42,57,86 Stepper within 3A  2/4 -phase / 4 wire / 6 wire stepper motor • automatic half-decay • excitation mode: synchronizing, half step, 1/8 step, 1/16 step • current level is adjustable to meet your application needs • large heat sink for good heat dissipation • overheating and over-current protection circuit to ensure optimal performance, operating voltage: 10 to 35 VDC • rated output current: ± 3 A - peak 3.5 A • dimensions: 50 x 75 x 35 mm • weight: 80 g