This is my first Multi-component project.....

 While searching for a dog themed leash holder, I decided to have a go at it myself.  The back plate is leveled and anchored into the wall, the two screw holes are chamfered and recessed. Once mounted, the outer shell then snapping over in two pieces, allowing for a total length bigger than what the printer could support.  The four pegs go through the shell and screw into the backplate, their graduated shape locks the outer shell against the backplate.

Everything was printed with rectilinear 15% infill except for the Pegs which were set to 50% for strength and wall loops from 2 to 4.  That setting, their shape and the 12mm threads, is more than sufficient for anything hanging on them with regular PLA.

Note that the wall loops could be set from default of 2 to 4 when printing the wall mount to provide better support for the threads for the pegs.

Designed on Freecad 0.21.2 
Drafted on my P1P to P1S conversion [official]

Thread tolerance for Peg is 
.990 Scale with -.5 offset.
If you have a printer that still has issues screwing in the peg try the Peg - Loose-Fit
.990 Scale with -.75 offset

Included photos show diameter measurements of outer threads at these offsets.