4" x 2" Polyurethane on Aluminum Wheel Caster with 3/4" x 4" Threaded Stem - 600 Lbs Capacity4" x 2" Polyurethane on Aluminum Wheel Swivel Caster With 3 4" Threaded Stem Part #: 7RTP043P7 Polyurethane wheels offer more floor protection, non marking treads, quieter rolling, & smoother rides compared to steel or phenolic wheels while still providing comparable load capacities. Polyurethane on aluminum caster wheels are considered the premium polyurethane wheel. These caster wheels offer all of the benefits of polyurethane on iron wheels, and