SR4ZZ Stainless Steel Premium ABEC-5 Ball Bearing with Si3N4 Ceramic Balls (Silicon Nitride) 1/4" x 5/8" x 0.196" inch SR4ZZ Stainless Steel Ball Bearing with Ceramic Balls Premium ABEC-5 quality, this is a popular size that could be used in many application that uses this size 1/4" x 5/8" x 0.196" inch. Bearing is made of Stainless Steel, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, Ceramic Balls are the highest standard of balls that can make your bearings live at least 5 times more than any other bearings.