This braket hold two curtain rods (20mm).
To secure the rods a hole to tap a M3 thread is foreseen. After taping the hole you can use M3x6 or longer bolts to secure the rods.

To tap a hole on a 3D printed part is very easy, all you need is a small power drill and the cheapest chineese taps you can find online. an instruction how to tap (the fast&dirty way) https://www.youtube.com/watch?v=vb6mAQ-s73A

One hole is very deep so I had to use a tap extension. Check it out here: https://www.thingiverse.com/thing:3388344