This 4" x 1-1/4" Thermoplastic Round Gray Tread on Kingpin Swivel Caster consists of pressed steel, with ball bearings. Features: Bolted wheel axle and Zinc-plated. This caster includes rich-quality thermoplastic polyurethane, low-noise operation, low rolling and swivelling resistance, proper floor conservation, and very high chafing resistance. In addition it is chemically bonded for an indivisible linkage to the wheel center.