Ball retainers *Certificates:ISO9001 *Material:Bronze,Aluminium,POM; * ... and prolong service life.6.sound quality steel ball retainer with excellent performance of hardness,glossiness,buildiness, ... made of other material ,just like ceramic,plastic etc.)NO 1: Plastic bushing (blue,white colour,POMS,POMBS,POMM ... glad to give you the best service. ball cage, ball retainers of brass for mould accessories