... side damage on machine parts and prolong service life.6.sound quality steel ball retainer with excellent performance of hardness ... ceramic,plastic etc.)NO 1: Plastic bushing (blue,white colour,POMS,POMBS,POMM,POMBM,POMT,POMBT type;NO ... 2:Aluminum bushing(white,cupreous colour,ALBS,ALS,ALBM,ALM,ALBT,ALT type ... you the best service. different model of big size ball bearing