The material of ring is POM,the cage is nylon,the balls have glass balls or stainless steel balls. The material of ring is POM,the cage is nylon,the balls have glass balls or stainless steel balls.The model include:POM 608~POM609POM 626~POM629POM 6000~POM6010POM 6200~POM6210POM 6300~POM6310 Plastic bearings