1.good wear resistance 2.Good elasticity 3.High precision, high concentricity 4.No bubbles 5.Smooth surface DescriptionPU ... to 300°CHub MaterialAluminum, Steel, Sintered Bronze, Brass, Bearing, Many PlasticsBearing ChoicesBall, Needle, Sintered Bronze, PlasticWarranty6 months ~ 12 monthsSpecial ... needs Soft wear resistant PU wheel with axle shaft, High quality (Many hardness)