This is a snap-fit double hat hook that hangs on an 8 mm diameter round railing. (If you don't know the diameter of your railing, a cheap round BIC pen should be approximately 8 mm in diameter. You can compare the size of the pen to the railing.)

This hook works for two hats or just a single hat (see pictures).

I've successfully printed 8 of these with essentially default Cura "Standard Quality" Ender 3 settings at 20% and 30% infill.

Any feedback or suggestions are appreciated.