Well, looking at it, DS games are backwards compatible on the 3DS. Therefore, the 3DS cartridges should be the same size. Or the place you insert the cartridge could be larger than the DS's slot but the DS cartridge could still fit.
looks to me like its the same size, but it has a little knob thing to the side, which prevents you from putting it in a DS, meaning it probably wont fit the same cases if they are the exact same size of the ds games, the little knob thing will probably make it not fit
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