Features These linear motion bearings are manufactured from a high quality aluminum alloy to offer low noise and long service life. The bearings have an inner diameter of 20 mm, an outer diameter of 39 mm and a thickness of 11 mm. They are ideal for 20mm shaft/rod projects, such as 3D printers and engraving machines. They are open-type blocks, have high speed and high precision. They come a total of 4 bearings that you can use for many different projects. 1. These linear motion bearings are made of high quality aluminum alloy to offer low noise and long service life. 2. The bearings have an inner diameter of 20 mm, an outer diameter of 39 mm and a thickness of 11 mm. 3. They are ideal for 20mm shaft/rod projects, such as 3D printers and engraving machines. 4. They are open-type blocks, have high speed and high precision. 5. Comes with a total of 4 bearings that you can use for many different projects. Specification: Features: These linear motion bearings are made of high quality aluminum alloy to achieve low noise and long service life. . The bearings have an inner diameter of 20mm, an outer diameter of 39mm and a thickness of 11mm. They are ideal for 20mm shaft/rod projects, such as 3D printers and engraving machines. They are open-type blocks, have high speed and high precision. It comes with a total of 4 bearings that you can use for many different projects. Specifications: Type: SBR20UU Material: aluminium alloy. Inner diameter: 20 mm/0.8 inches. Outer diameter: 39 mm/1.5 inches. Thickness: 11 mm/0.4 inches. Quantity: 4 pieces Package includes: 4 x Linear Blocks Package List