This flexible Shaft Coupler is design to mate between 6.35mm and 8mm shafts

The DM542A is a type of two-phase hybrid stepping motor driver for one motor. It is designed for use with 2-phase hybrid stepper motor of all kinds with 42mm to 86mm outside diameter and less than 4.0A phase current.
Input Voltage: 18VDC to 50VDC.
Input Power: <4A up to 80W
Output Current: 1A - 4.2A(peak)
Inputs and Outputs are opto-isolated.
Overvoltage, under voltage, overcorrect, phase short circuit protection
Operating Temperature: -10 to 45 degreesC
15 channel subdivision and automatic idle-current reduction. 8 channels output phase current setting
Replaces the older MD542 Driver