After removing one side of the collapsible storage crate, this model can be used to slide over the edges of two adjoined crates to keep them together. The wooden dowel goes through all the parts to add structure against bending from the tension of the bungee cords.
The “spacer” part is optional - just a little frame to prevent the boxes from moving around, it also provides additional storage space on both ends of the shelf, where reaching from the front is not feasible.
The recessed anchors are for threading through 1/8inch bungee cord.
This is very specific to a small storage crate that I happened to have:
(at the time of writing the “small” size doesn't seem to be available)
The author marked this model as their own original creation.