The 203mm mecanum wheel is a heavy duty wheel comprised of a series of rollers, mounted so that their axis of rotation is 45 to the axis of the main wheel. As the wheels rotate in sync, the vehicle moves forwards or backwards normally, but by spinning pairs of wheels in opposite directions, the rollers enable sideways movement. Put it all together and you can move laterally, diagonally, or spin in a circle. Along with 4 assembled wheels, twelve bolts and twelve nuts are included for bolting on to either the 6mm Nexus aluminum wheel hub or the 8mm Nexus aluminum wheel hub.