Here is another alternative to the Pneumatic (air-filled) caster. Our 3419-6X2 (rigid caster) has a load capacity of 250 pounds and has the standard 4 X 4-1/2″ Top Plate. These casters will fit most industrial carts and large Rubbermaid service carts, to name a few. Give us a call for more info. or stop by our showroom and take a look for yourself. Flat Free Rigid Caster