MR63ZZ Shielded Ball Bearings 3mm x 6mm x 2.5mm 10 Ball Bearings MR63ZZ Shielded Ball Bearings, the inner diameter is 3mm, outer diameter is 6mm and the width is 2.5mm, Bearings are made of Chrome Steel, each bearing has 2 Metal Sheild to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.