I saw a helpful hands-free 90* corner brace to help when joining two pieces of wood, and decided I needed to reproduce it. By placing the corner clips on your box corners and adding some reinforcement from your own clamp, you'll bring the corners of your box together at a perfect 90-degree angle, ready for simple outside butt joining or inside pocket hole joining.

Instead of creating two separate pieces for the top/bottom; I just use the 'reflect' option in my slicer, and print one of each.

Size fits a standard 3/4" piece of lumber, or scale up or to accommodate your unique project.