The trailer wheel dock / receiver is designed to stabilize your trailer by holding the front jack wheel in position on any surface - pavement, sand, grass, etc. Acts as a multi-directional chock. Great for any type of trailer, eg. camper, RV, caravan, boat, jetski, etc. Fits all sizes of single front trailer wheel / trailer tongue wheel / jockey wheel / jack wheel. Made of rigid blue plastic. Approximately 12 inches wide by 2 inches high.