SR4ZZ Shielded Stainless Steel Premium ABEC-5 Ball Bearing With SI3N4 Ceramic Balls 1/4" x 5/8" x 0.196" inch SR4ZZ Shielded Premium ABEC-5 Ball Bearing, bearing is Stainless Steel bearing SI3N4 Ceramic Balls, Bearing is made of Stainless Steel and has Solid Ceramic balls (SI3N4).