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: U624ZZ Inner Diameter: 4mm / 0.15 inch Outer Diameter: 13mm / 0.51 inch Height: 7mm / 0.27 inch U Groove Width: 5.2mm / 0.2 inch U Groove Depth: 1.8mm / 0.07 inch colour:Silver Material:Carbon steel size:13 x 7 x 4mm Package contents: 100 x Bearings Only the above package content, other products are not included. Note: Light reflection 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.