R4AZZ Shielded Ball Bearings, the inner diameter is 1/4", outer diameter is 3/4" and width is 9/32", R4AZZ Bearings are made of Chrome Steel, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease, Bearings are packed 10 bearings in one plastic tube.