IMPORTANT: I made this to specifically fit these clear case protectors for my 3DS and DS games: https://www.amazon.de/dp/B07WLW5MDJ?ref=ppx_yo2ov_dt_b_fed_asin_title

The size of the clear case protector that fits into the slots of the model i made are:
 

And also a thickness of about 6 mm, but that is less important as it has a bit of buffer.

Hope someone else can enjoy this too, as I only specifically made them for my use case, but thought maybe someone else would like it too!