I had a Proline and Fretrest guitar mount that I wanted to match.  I designed this to resemble those wall mounts.  You will need a 3-inch ¼ - 20 bolt and nut or similar.  I wanted to use a bolt and nut for strength so I didn't wake up to a guitar that had fallen.

For strength purposes the arm needs to be printed flat to allow the layer strength to be sturdiest in horizontal position.

There are two posts.  1 is a standard post and the other is fitted to sit nicer with the arm portion.

I used PETG filament, but I imagine it would work with PLA as well.