Cover for drill holes in furniture and walls.
Low profile but still thick enough (0.6mm) to make colors work.
Sizes 4 to 22 millimeter in 1mm steps are available.
From 22mm on and larger, my advise is to use this much sturdier design:
https://www.printables.com/model/795303-hole-plug-cover
The author marked this model as their own original creation.