3/8" x 5/8" x 3mm Ball Bearing One Bearing; 3/8" x 5/8" x 3mm Shielded Ball Bearing, this is a popular size that could be used in many applications that uses this size 3/8" x 5/8" x 3mm. Bearing is made of chrome Steel, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearing is pre-lubricated with grease.