1,These liner-motion bearings are made of aluminum alloy for low noise and long service life. 2,Bearings have a 20mm inner diameter, a 39mm outer diameter, and a 11mm thickness. 3,These are great for 20mm shaft/rod projects such as 3D printer, engraving machine. 4,They are open type blocks, have high speed and high precision. 5,There comes total 4 pieces bearings which you may use for many different projects. Features: These liner-motion bearings are made of aluminum alloy for low noise and long service life. Bearings have a 20mm inner diameter, a 39mm outer diameter, and a 11mm thickness. These are great for 20mm shaft/rod projects such as 3D printer, engraving machine. They are open type blocks, have high speed and high precision. There comes total 4 pieces bearings which you may use for many different projects. Specifications: Type: SBR20UU Material: Aluminum alloy Inner Diameter: 20mm/0.8in Outer Diameter: 39mm/1.5in Thickness: 11mm/0.4in Quantity: 4pcs Package Includes: 4 x Linear Blocks Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement. Sold by-DIMEANI official store