This eccentric painting hanger is used to level paintings to correct imperfectly drilled holes.
Just fix a pair of it to a wall and tighten just so you can turn it with a little force but it won't turn when under load.
Then use a 4mm hex - the iconic 4mm IKEA hex supplied with virtually every IKEA furniture piece works well (as designed) - to adjust the pair to be level. Mount your painting and enjoy!

The model is designed to be used with flat head screws at 5mm diameter and be printed at 0.2mm layer heights as it uses "sacrificial bridging" to eliminate the need for supports. Just poke the single layer blocking the bore through and you are ready to go.
If need be I'll happy to provide a version for countersunk screws as well.
If you require different screw diameters just scale accordingling.