I made this cool guitar hanger with invisible screws. The mount itself is printed with GreenGate's "Devin Montes Cool Grey" 100% Recycled PETG Filament, and the top padding is printed with a flexible TPU like Ninjaflex

Use the wall-plate to trace screw placement on your wall. Screw into a stud for best strength, or use quality anchors. Of course the strength will also come down to the print quality. I printed the PETG at 100% infill and it feels more than strong enough for my acoustic guitar, but use at your own risk! Make sure the arrow on the 'wall-plate' is pointing upwards, and use at least the top and bottom screw holes (middle if you want the extra strength)

The 'padding.stl' should friction fit onto the 'arm.stl' which slides onto the 'wall-plate'. If the flexible padding doesn't stay in place you can also glue it down with E6000 adhesive.

I've included versions to fit varying guitar neck widths. The 50mm, 56mm, and 60mm versions indicate the maximum width at the first fret.