BQLZR 8mm to 12mm Flexible Clamp Jaw Shaft Coupling CNC Stepper Motor Coupler Router D25L30 CNC Stepper Coupler High quality aluminum coupler is widely used to connect servo motor, stepper motor, encoder, screw driving, machine platform, etc. The Coupler is zero backlash,and Designed to help compensate for misaligned parallels and axial. Shaft coupler used to connect servo motor, stepper motor, encoder, screw driving,ect Shaft: 8mm X 12mm(0.315" x 0.472").