The EasyMech 6mm Al Coupling For 58mm Plastic Omni Wheel allows you to mount robot wheels and mechanisms to motor shafts. This coupling is designed to connect Plastic Omni Wheel with a DC motor. Compatible With: 58mm Plastic Omni Wheel for Lego Specifications and Features: Used to connect the robot Wheel and a DC motor Material: Aluminum-alloy Outside diameter: 14.2mm Inside diameter For Motor Shaft: 4mm Net weight: 14g   Package Includes: 1 x Easymech 4mm Al Coupling For 58mm Plastic Omni Wheel 1 x Accessories Set Category: Couplings