Similar to rigid clamp couplings, shaft couplers are used to hold bearings and sprockets tightly on the shaft, and are used in motor and gearbox assemblies. Uxcell 2pcs Shaft Coupling 5mm to 8mm Bore L25xD14 Robot Motor Wheel Rigid Coupler Blue Top tight type rigid coupling,high torque with rigidity, low inertia and excellent sensitivity. Single piece set screw clamp design makes it easy to set up the items on the shaft and control the holding capacity of the coupling. Connection Bore Diameter: 3mm to 8mm; Total Length: 25mm /0.98 inch, Outside Diameter : 14mm/ 0.55 inch; with M4 Screws · Widely used in blowers,3D printer,DIY... Widely used in blowers,3D printer,DIY robots,CNC machine,stepper motors,etc. Aluminum Rigid Shaft Coupler Uxcell 4mm To 4mm Bore Rigid Coupling Set Screw Qatar Set Screw Clamp Coupling Specification:Connection Bore Diameter: 3mm to 8mmTotal Length: 25mm /0., 98 inchOutside Diameter : 14mm/ 0., 55 inchThrough Angle: 180 DegreeMaterial: Aluminum AlloyColor: BlueScrews Size: M4*4mm (D*L)Package Content:2 x Rigid Shaft Couplers8 x M4 Screws No rotation gap, elastic action can make up for symmetrical angular misalignment.