This is a very simple card holder, it's the 4th version I drew. You can slide cards out from both sides. This was designed so that you can browse cards from a side and pull out the one you need from the other side.
As for every card holder, it will feel kind of hard at the beginning, but it will get easier with use. It fits M4 screws and nuts. I used 15mm screws, and it fits 12 cards. No glue, no sopports, more or less 2 hours to print all pieces. I recommend to use a drill to get the holes more even before fitting the screw.
No particular setting for the printer, I set like 65% infill because I wanted it to be quite sturdy.
I used 6 walls, because this will make holes and bending "wings" more durable (at least I hope so).

Enjoy!