Dual Wheel Polyurethane (Sirius) Casters / Highly Ergonomic Upgrade Casters are the New X-Treme Ergo Is An Industry Leader In Ergonomic Performance. Made Of Premium Grade Polyurethane, The Independent Dual Wheels Allow For Sharp Turns With The Smallest Radius. Coupled With An Industry Changing Double Precision Raceway, For One Of The Tightest Swivels Produced. The 6203 Premium Precision Ball Bearings Ensure Additional Strength, Ease Of Mobility, And Quietness. The Upgraded, Lightweight, Water Resistant Aluminum Core Makes It One Of The Lightest Casters In Its Class, While Standing As The Class Leader In Capacity. Finally, This Ultimate Caster Is Topped Off With An Anti-Corrosive, Moisture Resistant, Chrome Plated Finish.