HIGH QUALITY: These bearings are made from high quality carbon steel for durability and have a long service life.DOUBLE SHIELDED: These mini ball bearings are double shielded to avoid contaminants entering and save lubricant.U GROOVE: Bearings have a 1.8mm deep U groove that generally ride on a rail or track.PERFECT FOR LINEAR SYSTEM: These are bearings that are used in many linear motion systems.Model: U624ZZInner Diameter: 4mm / 0.15 inchOuter Diameter: 13mm / 0.51 inchHeight: 7mm / 0.27 inchU Groove Width: 5.2mm / 0.2 inchU Groove Depth: 1.8mm / 0.07 inchcolour:SilverMaterial:Carbon steelsize:13 x 7 x 4mmPackage contents:20 x BearingsOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.