Rugged Construction CargoChock. Fits standard wheel chock holder. (Chock Holder has to be purchased separately) Product Spec: Material HDPE Length: 470mm Width: 200mm Height: 230mm Weight:2kg. Please note - These wheel chocks are intended to be used when Tractor or trailer units are parked on an incline, as a safety precaution. They are not intended to prevent vehicles driving forward (for instance while being loaded in a yard) where the surface is flat, as they are likeley to simply get pushed along as the vehicle travels forwards. a rubber chock must be used for this purpose - please ask.