The wheels come in two halves. Aluminum tubing (not included) is bonded through the center to act as a hub. This allows you to select the hub size to fit your models axle size. The wheels are very light and do well on grass surfaces. Paved surfaces tend to wear the black paint off and weaken the wheel halve bond. Electrical tape has done a fair job improving traction when applied around the tire portion of the wheel. All the kits come in sets of two wheels and require assembly and painting. Plastic model cement, acrylic or enamel paints are recommended however, polyurethane coatings can be used if applied in thin coats.