Set of 10 Ball Bearings R188ZZ 1/4" inch x 1/2" inch x 3/16" inch 10 Bearing R188ZZ Shielded Bearings, the inner diameter is 1/4", outer diameter is 1/2" and the width is 3/16", each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.