This coupling makes it capable to connect a motor with a 4mm shaft to a wheel, i.e. mecanum wheel, or other object with the same hub pattern that needs to be rotated. Specification: Material: Aluminum Alloy Inner Diameter: 4mm Outer Diameter: 15mm Flange Diameter: 28mm Length: 16mm Part List 1×Flanged Coupling Φ28mm H16mm 2×Set Screw M3*5 (1 Backup)