6" x 2" Energy Saver Polyon Cast Wheel Rigid Caster - 1,250 lbs. capacity6" x 2" Energy Saver Polyon Cast Wheel Rigid Caster Crowned polyurethane elastomer tread chemically bonded to a solid heavy duty cast iron core. Combination of crowned tread and heavy core, offers higher weight capacities, durability and greater mobility than standard Polyon wheels. Tread: Polyurethane Elastomer Tread Chemically Bonded To Cast Iron Core Core: Heavy Duty Cast Iron Bearing: Roller Bearing Rig: Zinc Plated Rigid Caster, 4" x 4 1 2"