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