... .005~0.008Shrink fit : 0.012~0.0005mmMaterial: plastic (resin ),aluminum alloy(bushing),copper(bushing),steel(ball).Hardness ... causing by rolling contact and side damage on machine parts and prolong service life.6.sound quality ... made of other material ,just like ceramic,plastic etc.)NO 1: Plastic bushing (blue,white colour,POMS,POMBS,POMM ... to give you the best service. POM plastic bearing in China