Cover cap for (pre-)drilled holes. Updated 29-aug-2018.
Use it in your kitchen cabinet to keep it clean and more water-resistant (you don't want water in your particle-board). Or use it for any other hole you want to cover.
Update: From version 2 on, larger plug-diameters (>25 mm) are also working (tested at 40 mm). So you can use it for end-caps for pipes for example. Don't make the length of the plug too short for larger diameters or it will snap off. To be save (I hope) and if you can, use at least a plug-length of 15 mm for diameters larger then 20 mm.
It's a tight fit but still removable if you want (of course that's on my printer).
The cap is almost fully customizable in the Thingiverse-customizer or in OpenScad.
For your convenience there are also four stl's for 5 (ikea), 6 (other brands) and 8 mm (most popular dowel).
Slice it with concentric infill for the best and smoothest result for smaller diameters (<12 mm).
It's a small part so you need good bed-adhesion.
I tested it from 5 mm and up, they all gave a good result.
No support needed.
PLA works fine.
Happy covering :)
Update 28-aug-2018: cleaned the scad-file a little, same functionality.
Update 29-aug-2018: Plug got loose from the cap with higher diameters (>30 mm), problem solved. Functionality still the same, also working for larger diameters now.
More information about the fantastic and challenging program OpenScad can be found here: https://en.wikibooks.org/wiki/OpenSCAD_User_Manual