No top level categories exist.
   
1. Wheel Diameter (also called Wheel Size):
The vertical distance between two directly opposing points at the top and bottom of the wheel.
2. Bore Diameter:
The vertical distance between two directly opposing points on the inner edge of the space through the center of the wheel.
3. Face Width (also called Tread Width):
The width of the wheel tread cross section, measured at the base of the tread rather than at the point of contact with the floor.
4. Hub Length (also called Hub Width):
The horizontal distance between two directly opposing points on the side edges of the wheel's hub.
* These loose definitions are based upon the wheel's orientation in the image above.