6304-2RS Sealed Ball Bearing 20 x 52 x 15 mm 6304-2RS Sealed Ball Bearing, the inner diameter is 20mm, outer diameter is 52mm and the width is 15mm, Bearing is made of Chrome Steel, each bearing has 2 Blue Rubber Seals to protect the bearing from dust or any possible contamination, also bearing is pre-lubricated with grease.