These Aluminum shaft couplers allow you to couple two size shafts together. They can be used for connecting motor shafts to drive shafts, or two different-sized shafts. One-piece design allows flexible coupling to achieve a zero clearance to transmit torque and no maintenance advantages. Flexible coupling is the preferred product, In many stepper, servo system, Practical applications. Specification: Length:24.5mm Diameter: 19mm Bore A: 5mm Bore B: 8mm Part List： 1 x Aluminum shaft couplers 4 x Net 1 x Allen driver