After printing, heat the arms with a heat gun or a hair dryer and bend them to fit your head.
The initial design (the one part one) did hold up for a month or two, but it did brake after some time at the mounting point to the glasses. So there is now a stronger version with two parts that need to be glued together.
After some rough play with my children, these also broke, as everything will when enough force is applied. So I made some 3D printed guides for filing the screw plate out of aluminium.
Tools → Side for filing the overall shape with needle files and drilling the 1.8 mm hole.
Tools → Thickness for filing a 2mm flat extrusion to the right thickness
As you will damage the printed tools, it is a good idea to print several out so you can always check the fit with an undamaged piece. The tools are also parametric.
In a pinch, I would suggest going with the one part version, which is easier to assemble and strong enough for a few days or weeks.
28.01.2024 Initial Version
15.06.2024 Added Version with separate Screw Plate for a stronger product
The author remixed this model.
Made into Step/Fusion360 file and changed the geometry to fit my glasses.