This is a remix of Question Block 3DS/NDS Cartridge Case by zembacraftworks (https://www.thingiverse.com/thing:2755583)
Overall Dimensions 57.6 x 57.6 x 57.6 (mm)
Holds both NDS and DSi games
Holds 11 games
You may have to adjust the Lid Dimensions depending on your printing tolerance (Mine is set to 0.1mm).
I've added to Fusion360 File so you can remix it.
Update (22/11/18) included a second Lid with 0.05 gap
Overview and Background