5" x 2" Polyurethane on Iron Wheel Swivel Caster with 3/4" Threaded Stem - 600 Lbs Capacity5" x 2" POLYURETHANE ON IRON WHEEL SWIVEL CASTER WITH 3 4" THREADED STEM Part #: 7RTP052UIR Polyurethane on iron caster wheels offer more floor protection, non marking treads, quieter rolling, & smoother rides compared to steel or phenolic wheels while still providing comparable load capacities. These polyurethane on iron wheels are going to be more durable & heavier duty than a polyurethane on polyolefin wheel, but heavier and slightly more difficult