POM Spiral ball cage size customized Hardness: 62~67HRC steel ... 004lowµ:0.005~0.008Shrink fit : 0.012~0.0005mmMaterial: plastic (resin ),aluminum alloy(bushing),copper(bushing),steel(ball).Hardness: 62 ... can made of other material ,just like ceramic,plastic etc.)NO 1: Plastic bushing (blue,white colour,POMS,POMBS,POMM,POMBM, ... Joann).I'm glad to give you the best service. POM plastic bearing in China