Pack of 10 SR188ZZ Stainless Steel Ball Bearings, this is a popular size that could be used in many application that uses this size 1/4" x 1/2" x 3/16" inch. Bearings are made of Stainless Steel, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.