Durable polyurethane rubber construction rolls easily under heavy loads.About the EZ Roll Flat Free WheelThe 10 in EZ Roll Flat Free Wheel uses Microcellular Polyurethane rubber that requires no air and never goes flat. This is a maintenance free whe el that provides a smooth ride using semi-precision sealed bearings. Zirk fitting allows you to easily grease the hub as needed. The EZ Roll is a trusted product that will provide reliable service and fits virtually any hand truck with a 5/8 inch axl e