See also: Large and medium size options.
These little hooks are a perfect everyday household version of my Strong(er) cable wall hook.
They've been designed to hold everyday items like spray bottles, soap containers, hats, coats, etc. The hole clearances are ~4.2 mm, and they fit 2x common #8 screws perfectly.
Shown here printed in Prusament galaxy black PETG with 6 walls and 5 top/bottom surfaces.
PLA probably also works well, but depending on how heavily you load them, you should monitor the hooks for creep over time (a known issue with PLA) (use common sense here and it will be fine).
If you want something super-strong I recommend printing in polycarbonate, PACF, or similar engineering filaments with high tensile strength and stiffness. I've printed a few in Prusament PCCF and they're very rigid and strong, and I couldn't made them bend with my hands if i tried.
If printing in PETG, you may wish to use a small brim or mouse-ears. The relatively small surface area of contact may cause warping without them. I used a strongly-sticking textured PEI plate and I had 1 of 4 start warping during the print w/out using mouse-ear style brims.