The floor safe polyurethane tread on an interlocked polyolefin core is a lightweight and high capacity wheel. Polyurethane tread resists flat spots from long periods of inactivity.This smooth rolling and quiet wheel is resistant to oil, grease, water, and most solvents. Series 30 casters use tough bright zinc plated components such as heat treated double ball bearing raceways, 5/8" bolted king pin, 1/2" axle bolt, and 1/4" cold forged steel top plate and fork construction. Wheel tread hardness of 90-95 Shore (A) Durometer. For more caster options, including bearings and top plates, please call our sales team in West Reading, PA, at 1-800-215-8220.