Reference the original: http://www.thingiverse.com/thing:33706 Like Maikalguy's adapter, but I notice the 4xAA package is bigger than a single D cell, and wouldn't fit inside my Mag Flashlight! So this 3xAA adapter is slim enough to fit. I have some additional mods to this coming, too.Couple of layers, 10% fill should be fine for build. Wire it up like Maikaiguy shows in his version that this is a remix of; I only made one version, just copy that. Should use AWG24 wire. VERY IMPORTANT: The cells that go into this have to be the same. In the same state of charge, same manufacture. To be safe, they should be from the same box. Rechargeable cells should also be from the same box, and have the same number of charge/discharge cycles on them (i.e. used as a set, or of course new).