Unifi NanoHD on concrete ceiling - which box to provide?

I have also thought about printing. But I wonder if the print wouldn’t break when screwing?!

You don’t have to tighten the mounting plate firmly. Hand tight is enough! Possibly a bit more material around the screw area.

On Thingiverse, you can definitely find adapters under the keyword NanoHD. For example, under the ID 4090734. Screws hold great in 3D prints. They don't have to bear any weight, and screw holes are usually already included in the models. Without a 3D printer, I would work on a thick wooden board with a fret saw. In the non-visible areas, a jigsaw would also work. Then sand everything and paint it white. It's just a circle as the outer diameter and a rough inner circle to make room for the cable.

I don't know how it is with the Unifi APs, but maybe there is even a mounting ring included that can be used as a template.

I quite like the print. That's a great idea. I just don't want to lead the cable out of the adapter like in the example anymore. But that can be done. The mounting ring can really serve as a template there. Then I'll have our designer draw it.

I remember that someone here already did that once. Unfortunately, I can't find any idea on how to build/implement it easily and without much effort. Does anyone have an idea or, even better, a ready-made solution that I can replicate 1:1?

I suppose you mean my post here?

Exactly what I meant. I think it's cool. But I'm hesitant because I neither have the right tools nor the (probably) craftsmanship skills. Therefore, the printing is really a great alternative. Were the ordered plates 18 cm in diameter? Where did you order them?