Features 1、These liner-motion bearings are made of high quality bearing steel for low noise and long service life 2、They are double sealed to avoid contaminants entering and save lubricant 3、Bearings have a 12mm inner diameter, a 21mm outer diameter, and a 30mm height 4、These are great for small hobby 12mm shaft/rod projects such as 3D printer, engraving machine 5、There comes total 10 pieces bearings which you may use for many different projects Specification Features: These liner-motion bearings are made of high quality bearing steel for low noise and long service life. They are double sealed to avoid contaminants entering and save lubricant. Bearings have a 12mm inner diameter, a 21mm outer diameter, and a 30mm height. These are great for small hobby 12mm shaft/rod projects such as 3D printer, engraving machine. There comes total 10 pieces bearings which you may use for many different projects. Specifications: Type: LM12UU Material: Bearing steel Inner Diameter: 12mm / 0.47" Outer Diameter: 21mm / 0.83" Height: 30mm / 1.18" Quantity: 10pcs Package Includes: 10 x Bearings Package List