The 60mm aluminum mecanum wheel is the smallest size mecanum wheel in all of our mecanum wheels, the set of 60mm mecanum wheels includes 2 left wheels and 2 right wheels. It is a LEGO compatible mecanum wheel, it comes with an NXT compatible hub and an axle centre hub for the arduino motors and wheels. You can also use universal hubs to connect the wheels and motor. It will give you more choice, each wheel is comprised of 8 rubber rollers, these axles and rollers are sandwiched between two aluminum plates, use these mecanum wheels on your robot, it can be able to forward/backward movement, but also side to sie. Using rollers set on 45 degree rotational axis parallel to the mai rotational axis of the wheel, all of you need to do is to add your drive motors, controller boars and batteries.