These liner-motion bearings are made of high quality 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.