This is a pretty generic and customizable part for building a box structure out of pipe. I used it to build a box out of very inexpensive EMT conduit.
Overview and Background
Corner Bracket Doohicky for pipe or conduit
I designed this to be able to build a box/structure to hang things from but I would recommend they not be too heavy, otherwise, I recommend looking at something like Maker Pipe.
Because it is customizable, you can plug in your dimensions for the pipe diameter, gap size, screw hole size, length and height.
Lesson Plan and Activity
I am not sure why I can't publish without adding a Lesson Plan.