Polyurethane chemically bonded to Cast Iron core. Popular wheel used in material handling applications. Offers good floor protection, is non-marking and provides a quieter ride than hard tread or steel wheels. The Polyurethane tread is resistant to most chemicals, grease, oils and water. The Cast Iron core gives the wheel considerable strength, however it can rust when exposed to water and some chemicals, and could crack in shock load applications causing failure. Polyurethane wheels perform the best in indoor applications on smooth cement floors but will perform well in other applications too. Zerk grease fittings come standard on the core and enable the wheel bearings to be lubricated without removing it from a caster or taking the wheel apart.