My son is making a screen using foam-core which is 5mm thick. I remixed these with a 6mm clip and chamfers on the inside edges to make putting them on easy. 6mm so that they slide back and forth easily. When remixing the STL files, I also had to fix some of the parts, but the end result should look the same.
I also created a thin wall to support the top of the clip so that supports don't need to be turned on. You might need to enable "detect thin walls" in your slicer to make sure they print, but once printed, they remove very easily, and provide great support for a clean bridge when printing the first floor layer of the top part of the clip.
The project also includes a dice tower with channels to hold the 5mm foam core board. You can find that here: