18.5 x 26 x 4 Shielded Ball Bearing One Bearing 18.5 x 26 x 4 Double Metal Shielded, radial, deep groove ball bearing,bearing is made of Stainless Steel,bearing is closed with 2 Metal Shields, one Shield from each side to protect the bearing from dust or any possible contamination,bearing is sealed and self lubricated,inner diameter is 18.5mm, the outer diameter is 26mm and the width is 4mm. Most common application is the Align RC helicopter engine.