I use the foldable crates from Albert Heyn for the storage of some supplies. I wanted to move the crate around more easily, so I added some casters without adding too much to the height of the crate. 

I found this small fixed caster and bought it here. The casters tiedly fit on the mount and are fastened by a small peg that I glued from the back with a drop of superglue. 

The mount was printed on a Prusa MINI+ with the printer setting “0.20mm SPEED” setting. The pegs were printed horisontal (for more strength) with the setting: “0.10mm DETAIL” and auto generated “snug” support. See the 3mf files for details. Both were printed with Poly Terra PLA.

This project had another goal for me: learning and using FreeCAD/Ondsel. Probably less material could be used. I'm open for suggestions.