FR168ZZ Flanged Ball Bearings with Ceramic Balls, this is a popular size that be used in many applications that uses this size 1/4" x 3/8" x 1/8" inch. 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 bearing live at least 5 times more than any other bearing.