A small wall hook, 22mm tall and 12mm wide, with an invisible mount. Requires a 3.5 or 4mm countersunk screw. 

There are two versions: the thin version is 5mm thick and the other is 7mm thick.

I printed the model as oriented in the .3mf file in PETG with the default 0.2mm quality profile in PrusaSlicer.

If you like the model, I'd love to see a make!