Made of premium aluminum material, it is durable and long lasting use. Main dimensions: D=19mm, L=25mm Shaft Size: 4, 5, 6.35, 8, 10mm, Example: 8mm x 8mm (inner diameter for two ends), 11 different inner diameter for your choosing Wide Application: For connecting different shaft diameters, perfect for connect servo motor, stepper motor, encoder, screw driving, machine platform, etc. Package Included: 5 x Flexible Shaft Coupling, Manufacturer: SUPERTOOL