Du-Bro Large Inflatable Wheels 5.5" Part No: 550RV. Smooth inflatable tires with positive seal air valves. Features two piece bolt together hubs and hub caps. Wheels can be inflated (or deflated) thru a tiny valve in the side of the tire. Axle diameter size 5/32 (4 mm). Ideal as "tundra" tires to give an authentic look.