I needed this, so modeled it and printed. The screw hole size is 7mm and 8mm. Both .stl-s  and .3mf-s are here. As I tested 6.7mm and 7.5-7.8 screw head are perfect match but curvature of inside makes sure every screw is tight. I used 7layers of perimeter and 25% of adaptive cubic infill, organic supports are preffered. 40 minutes of printing and there is perfect hook for the wall.