Four different size tyre diameters and two different size wheel hubs. Tyre size is printed on tyres for easy reference. (6) Small Wheel Hub (4) Large Wheel Hub (4) 20mm Diameter Pulleys (4) 100mm Travel Rubber Tire (4) 160mm Travel Rubber Tire (4) 200mm Travel Rubber Tire (4) 250mm Travel Rubber Tire 6x Small Wheel Hub 4x Large Wheel Hub 4x 100mm Travel Rubber Tyre 4x 160mm Travel Rubber Tyre 4x 200mm Travel Rubber Tyre (4) 250mm Travel Rubber Tyre