I needed a battery box for 3 AA batteries for a 3.3V micro processor project. Uses #6 nuts and has holes for 1/4" #6 bolts. The holes are not need but are there if you need to use them for the bolts. The batteries will have a tight fit, but after you insert the batteries a few times, it will push the nuts into the holes. I found that the bolts were not needed at all after I had printed it, but makes for a clean wire connection. Also, if you can get away without using the bolts, you will not have exposed battery contacts to the outside of the box.