... ball bearing retainer,which is excellent performance of hardness,glossiness,resistance,service-life. This product is made of copper or aluminum ... specifications for your choice, also called ball bearing cage,ball bearing bushing,ball bearing bush,ball retainer & Die parts & die fittings ... 0.002mmMaterial: plastic (resin ),aluminum alloy(bushing),copper(bushing),steel(ball).Hardness: 62~67HRC,spherical ...