The metal struts snap into the leg of the wheelchair frame and adjust to the height needed for your pet. Struts are adjustable within a range of 3 inches and come in 6 different sizes: 6″, 9″, 11″, 12″, 15″ & 18″. The foam wheels are perfect for all breeds and great for all terrains. They feature a dense foam interior with an outer rubber layer. These wheels will not puncture, they wear extremely well, and are easy to clean. Sizes available: 4″, 8″,12″ & 16″.