What is that?

This thing combined with other things can used to create a sturdy wall mounted thing with hidden screws.

In my case i simply combined two objects in Cura and printed it.

Hint

I uploaded two versions of the STL file, a tight and a loose version.

Loose: This version should slide in and out easy without any effort.
Tight: This version needs some tension to slide in and will take some effort to dissamble afterwards.

Keep in mind that can highly differ with Printer, Settings and Filament you are using, so i would advise to create an testprint beforehand.