These MaxxHaul Interlocking Wheel Chocks are designed for tandem wheel axles to assist in keeping trailer in place. Can also be used as a individual wheel chocks when interlocking system is detached. As a tandem wheel , it can be used with tires up to 26"" in diameter and minimum spacing of 7"" between tires. Constructed from durable hard plastic with UV protection and features rubber surface and rubber pad in bottom for increased traction. Overall dimensions as a tandem wheel chock: 18"" long x 8-1/4"" wide x 4-3/4"" high. Overall dimensions as individual wheel chock: 9"" long 8-1/4"" wide x 4-3/4"" high.