You need to print the parts with relative high infill to make them rigid and strong. I printed them with 66% infill and 0.2 mm layer height. BOM: 4 x M5 threaded brass insert 4 x M5 x 12 mm hex screw Instructions: 1. Print parts 2. Set the 4 inserts into the parts 3. Assemble box with the 4 screws