BQLZR 5 x 8 mm D19L25 Flexible Shaft Coupling CNC Stepper Motor Encoder Coupler Pack of 2 The Coupler is zero backlash,and Designed to help compensate for misaligned parallels and axial. 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: 5mm x 8mm/0.2 x 0.31" Size: 19 x 25mm/0.75 x 0.98"(Dia x L)