This is a linear bearing holder that was designed to be a direct replacement for the aluminium holder that is used in many 3d printers.
I wanted to be able to use 3d printed LM8UU size linear bearings but didn't want to dismantle the aluminium ones. to assemble them.
The bearings should be a tight(ish) push fit. Just file to fit if needed.
Plus this should be much lighter than the metal ones so less mass to move around.
After some testing, using the printed toothed linear bearings below, the printer is so much quieter.