Features: The bearing is made of high carbon chrome ball bearing steel which is of good hardness and strength. The roller way type of the bearing is spherical raceway. The inner diameter is 12mm,the outer diameter is 39.3mm and the thickness is 20mm. Fine polished surface provides great smoothness. Well craftsmanship provides durability and long service life. Specification: Item Type: Track Guide Roller Bearing Model:LFR5201-14 KDD/LFR5201-14 NPP(Optional) Size:(Inner Diameter x Outer Diameter x Thickness) 12 x 39.3 x 20mm / 0.47 x 1.55 x 0.79in Material:High Carbon Chrome Bearing Steel Roller Way Type: Spherical Raceway Package List: 1 x Bearing Package List 1The roller way type of the bearing is spherical raceway. 2The bearing is made of high carbon chrome ball bearing steel which is of good hardness and strength. 3The inner diameter is 12mm,the outer diameter is 39.3mm and the thickness is 20mm. 4Fine polished surface provides great smoothness. 5Well craftsmanship provides durability and long service life.