Features: These bearings are made from high quality carbon steel for durability and long service life. They are double shielded to avoid contaminants entering and save lubricant. Bearings have 1.8mm deep U groove that generally ride on a rail or track. These are bearings that are used in many linear motion systems.There comes total 10 pcs bearings which you may use for many different projects. Specifications: Material: Carbon steel Model: U624ZZInner Diameter: 4mm / 0.15" Outer Diameter: 13mm / 0.51" Height: 7mm / 0.27"U groove Width: 5.2mm / 0.2"U groove Depth: 1.8mm / 0.07"Quantity: 10pcs Package Includes: 10 x Bearings Note:Please note that the new type and old type of this product will be sent randomly, and make sure you will not mind before ordering..