This device holds a grid of 21700 batteries for making a battery pack. There are openings for easy wiring and holes for bolting it together. I found that 3" #6 round head bolts work, though they are a little bit too long. The number of 21700s can be set easily in the scad file and it could probably be modified for 18650 or other cells without much effort. Lithium batteries are dangerous and I am not an expert, use this at your own risk.
Download scad and STL files