Wheel chocks placed around an aircraft's landing gear.

Wheel chocks (or chocks) are wedges of sturdy material placed behind a vehicle's wheels to prevent accidental movement. Chocks are placed for safety in addition to setting the brakes. The bottom surface is sometimes coated in rubber to enhance grip with the ground. For ease of removal, a rope may be tied to the chock or a set of two chocks. One edge of the wedge has a concave profile to contour to the wheel and increase the force necessary to overrun the chock. Automobiles usually have parking brakes on the rear wheels. If the rear axle is jacked off the ground with only the parking brake set, the vehicle may roll on the front wheels and fall. Chocking the front wheels prevents this mishap.

An Airman prepares to pull the landing gear wheel chock of an F-117 Nighthawk fighter during an end of runway check at Kunsan Air Base, South Korea.

Motorcycle and bicycle chocks are bifurcated and fit around the wheel, supporting the bike and preventing its movement.

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