... and specifications for your choice, also called ball bearing cage,ball bearing bushing,ball bearing bush,ball retainer & Die parts & die fittings for ... 01~0.002mmMaterial: plastic (resin ),aluminum alloy(bushing),copper(bushing),steel(ball).Hardness: 62~67HRC,spherical degree is ... and prolong service life.6.sound quality steel ball retainer with excellent performance of hardness,glossiness,buildiness, ...