House numbers with hidden hardware

ABS or PETG recommended.
No supports needed.
I used 20% infill

I have the numbers reversed with the holes face up in order to showcase the keyhole placement but I found printing them with the holes facedown to work best.

I tried my best to have all the holes line up identically so that it would be easy to construct a template for hanging. However, I was foiled by the 7 and the 4, they just had to be different. I used 2 holes per number to help them stay straight but if you don't want to use both, you only need to install one screw and ignore the second keyhole.

Keyhole at this size will fit any decking screw or #8 screw. Numbers should be able to be tightly mounted as long as the screw is installed close to the wall.

Unfortunately adjusting the size/scale will distort the keyhole size. If this is the case you could possibly find different hardware that fits; or if you'd like to design your own numbers and sizes, use my keyhole file found here:
https://www.thingivers