12/7/2021 - I also have a folding version that holds 8 SD cards and doesn't need a slip case. It is here: https://www.thingiverse.com/thing:5170046
or here: https://cults3d.com/en/3d-model/various/sd-folding-case-holder

12/1/2021 - Redesigned the 4 SD holder so it fits in the same case. Also added a variant with 2 SD and 8 microSD. The YouTube video does not show the latest SD versions, I'll make a new one soon. I added both STL and the newer 3MF formats which are much smaller files.

This is a much improved version of my earlier SD cases found here: https://www.thingiverse.com/thing:4716706
The tolerances were too tight and the old one was often difficult to print so that the cards actually fit in the holes.
These now use a printed spring bar to hold the cards in place. Note that you might need to push on it or cut it free with a knife after printing it, sometimes it sticks to the bottom. I use a pair of pliers to gently snap it loose.
I have printed this on all my printers to make sure it works.
The cover case is best printed standing on end. You might need a raft if the bed adhesion isn't strong enough.
I made a video showing how to best insert the cards. https://youtu.be/p5fBX4f-1x0

I also have a folding one almost ready that holds 8 SD cards and folds in the middle like a wallet. It prints in one piece.

Ender 5 and FLSUN

No

No

0.2mm

20%