... or aluminum or POM resin base material and well arranged steel balls.The products are widely used in machinery industry, ... 0.002mmMaterial: plastic (resin ),aluminum alloy(bushing),copper(bushing),steel(ball).Hardness: 62~67HRC,spherical degree is 0.25UM.Features1 ... on machine parts and prolong service life.6.sound quality steel ball retainer with excellent performance of hardness,glossiness,buildiness, ...