Variation of Jer's design meant to be added to the outside corner of a box.  I'm using it to stabilize a table saw stand I built years ago that doesn't have any inside corners like the box shown in Jer's model, thus my desire for it to attach on the outside corner of the box.  A triumph of engineering to be sure!

The parts as uploaded here have 0.4mm thread tolerance.  Holes are countersunk for #6 screws.