Concrete plug / Beton Stoppel

The outer diameter of the plug is 24.6mm, and can be plugged into the concrete/plastic holes with a hammer very tightly.

I used PLA (since I use it in an area without rain or direct sunlight), using Prusament PLA Marble Grey; infill 30%, 2 walls.

Since the fit is very tight, you might have to scale it to 98% if you want to be able to remove the plug at some point in time without destroying it completely.