PU6x28x6 Tire PU Covered Bearing 6x28x6mm Sealed Miniature - tirePU6x28x6 Tire Polyurethane Rubber sealed Ball Bearing 6mm x 28mm x 6mm Polyurethane ( PU) is a new type of polymer composite materials between rubber and plastic, offering higher load bearing capacity compared to plastic, polyurethane offer superior impact resistance, while good mechanical properties. Polyurethane have better abrasion and tear resistance than rubber. PU6x28x6 Ball Bearing Deep Groove Ball Bearing Material: Cr15 bearing steel Cover