18650 D-Cell Adapter
thingiverse
This adapter replaces two D-Cells with one 18650 battery. I use it in my Mag Flashlights. You will need two battery tabs I use Keystone 209 clips from Amazon. The negative end I am using a quarter, but you can use a washer as well. I just didn't found it easier to solder a quarter. http://www.amazon.com/Keystone-Electronics-Contact-battery-spring/dp/B00LPOVJHS/ref=sr_1_2?ie=UTF8&qid=1451248043&sr=8-2&keywords=Keystone+209
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