This is a 50mm Omni directional robot wheel,it's useful as they roll freely, The 50mm plastic omni wheel is a robust,durable and double row wheel that provides easy 360°movement prope with rotational and sideways manoeuvrability. It comes with 3 different styles of hubs for the Arduino motors. If you use this omni wheel on your robot, it can be able to forward/backwards and rotation without changing its orientation.