Made of heavy pressed steel. Rugged hinged plate construction with maintenance-free steel spring mechanism. Bolted wheel axle. Zinc-plated, blue-passivated, Cr6-free. Made of high-quality, reaction-injected polyurethane-elastomer Blickle Extrathane®, low-noise operation, low rolling resistance, good floor preservation, very high abrasion resistance, high cut and tear propagation resistance, very good chemical connection with the wheel center.