Wheel Boards are designed to fit securely between the Uprights (ribs) allowing mobility of your Deltarack. They can be permanently secured to the rack, or simply held by the weight of the rack, enabling the wheel boards to be removed as needed. Each set comes with 2 swivel locking wheels and 2 fixed directional wheels. The wheels are high quality, pressed steel frame, with thermoplastic polyurethane wheel and tread. All hardware is included.