Checkers' 1800 Series Roadblocks Wheel Chocks are specifically designed for the mining and construction industries. They are strong, safe and lightweight yet hold the largest haul trucks. RoadBlocks Off-Road Urethane Wheel Chocks are made from tough, damage resistant polyurethane. They will not cause tire damage and are virtually unaffected by oils, fuels or solvents. For added safety and convenience, "How to Use" guidelines are molded into the back of each chock.