SR188ZZ ABEC-5 Ball Bearings Stainless Steel and Ceramic Balls 1/4" x 1/2" x 3/16" inch 10 Ball Bearings SR188ZZ Stainless Steel with Ceramic Balls ABEC-5 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, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.