The 811-7 Urethane Wheel Chock is light weight yet heavy duty. Molded urethane chock is contoured to fit truck tires. Designed to grip both the tire and the pavement. The 811-7 Urethane Wheel Chock will not harm macadam. Guaranteed to be free of defects in material and workmanship under normal conditions of usage, provided our recommended installation and maintenance instructions are followed.