This chock can also be referred to as a Wheel Stop. It is designed to fit between the tyres on a tandem axle caravan, motorhome, RV or trailer to stabilise the suspension, which eliminates sway, rocking, and other movement while parked. The chock is very easy to install - position it between the tyres and tighten using the knob on top until the top and bottom chocks are firmly in place. To remove, simply turn the knob the other way. Suitable for dual axles with a tyre spacing of 1-1/2= to 3-1/2= and tyres between 26= to 30= diameter. Note: These chocks do not replace brakes or wheel wedges to prevent the trailer or vehicle rolling.