Mold on polyurethane casters with cast iron core are superior to rubber casters in resistance to grease, oil, cutting, chunking, and abrasive wear. these caster wheels can be used on almost any factory floor. given the same size load on a smooth floor, a polyurethane caster wheel rolls easier than the same size conventional rubber caster wheel. any wheel color avaliable. straight roller bearing with drilled hardended steel spanner bushing.