10mm box. 2.4mm between openings so its exactly 2 walls with a .6 nozzle or 3 walls with a .4 nozzle Up to you. Lids do fit tight when printed at higher layer heights but do work looser over time anything under .2 works smooth right out of the printer. You could also do 100.5% scale on lid if you dont want to deal with the break in period.

Original idea from Battle Box but this is a J.A.T Designs Complete redesign for better printability, speed, and material savings. All my boxes are about 15-20% smaller physical size so you can fit more ammo in your safe.