What is this?The coupling shaft is made of 45# steel, suitable for connecting servo motor, stepper motor, encoder, screw driving, machine platform, etc.What will I get?The coupling shaft, we provide here, is in size of: Bore Diameter: 18mm to 20mm/0.71 inch to 0.79 inch; Length: 51mm/2.01 inch; Outside Diameter: 44mm/1.73 inch; Slot Width: 6mm/0.24 inch; Thread Size: M6*1; Color: BlackIn the package of 1 x coupling shaftAre there any advantages of the product?The flexibility of the coupling shaft joint removes stress between the motor and drive components. High hardness, durable, and excellent response, not easy to loosen.What should I notice?All size is measured by manual, please allow +/-0.1 inch error.