These project boxes have removable ends making it easy to modify.  There are also 2 extra ends for the mod which could also be used as a divider inside the box.  These are long enough to put an 18650, 2 18350, or 2 16340 batteries giving you the option to create a mod from 3.7 to 7.4 volts.  Very nice.  This box has a lot of possibilities.

 

Outside dimensions: 4.5" x 1.4" x 1"

Approximate inside dimensions: 4.2" x 1.2" x .75"