Wheel Chock
A wedge-shaped block placed against a vehicle's tires to prevent accidental rolling while raised or serviced.
A wheel chock is a heavy wedge of sturdy material (such as reinforced rubber, steel, or hard plastic) placed tightly against the tires of a parked vehicle. Its primary purpose is to block the wheels and prevent the vehicle from rolling or moving accidentally while it is raised on a jack, supported on jack stands, or parked on an incline during service.
Safety dictates that wheel chocks should always be used when raising one end of a vehicle. For example, if the front of a vehicle is lifted, the rear wheels remain on the ground and must be chocked. Because rear wheels contain the parking brake mechanism, raising the rear end leaves only the front wheels to hold the vehicle, which can easily roll if the transmission is not locked. Chocking the wheels on the ground eliminates this hazard.
Chocks are placed on both sides of the tire (front and back) to prevent movement in either direction. They must be sized appropriately for the vehicle; large trucks and trailers require heavy-duty industrial chocks with grip teeth on the bottom to prevent sliding on concrete shop floors.