Plastic ball bearing is a kind of precise mechanical component that changes the sliding friction between the shaft and the housing bore into rolling friction. It reduces the energy loss because of friction. Rolling bearings are generally composed of four parts: inner ring, outer ring, rolling elements and cage. The inner ring is to cooperate with the shaft and rotate together with the shaft; the outer ring is to cooperate with the hosing hole as a support; the rolling element is evenly distributed by the cage between the inner ring and the outer ring, its shape, size and quantity directly affect the performance and life of the rolling bearing; the cage is to evenly distribute the rolling elements, prevent the rolling elements from falling off and guide the rolling elements to rotate to achieve rolling lubrication between shaft and housing.