6N137 highspeed 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 halfdecay 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 overcurrent protection circuit to ensure optimal performance