5 x 12 x 4 Sealed Ball Bearing One Bearing 5 x 12 x 4 Sealed Ball Bearing, Bearing is made of Chrome Steel, each bearing is rubber sealed from both sides to protect the bearing from dust or any possible contamination, also bearing is pre-lubricated with grease, Bearing inner diameter is 5mm, Bearing outer diameter is 12mm and Bearing width is 4mm.