SR168ZZ High Speed Stainless Steel Premium ABEC-5 Ball Bearing 7 Solid SI3N4 Ceramic Balls 1/4" x 3/8" x 1/8" inch SR168ZZ High Speed Stainless Steel Premium ABEC-5 Ball Bearing with 7 solid SI3N4 Ceramic Balls, Bearing is made of Stainless Steel and has Solid Ceramic balls (SI3N4).