I made many Lockable Present Ornament, many of then wrapped at beginning.
They are waste? No, I looking for what they can do at their rest life time, maybe a pencil holder. Finally, I find Sewing box by NicApicella.
These small steel plates come from my daughter's assembling toy, thanks to her :)

I didn't design the assemble, just drill holes directly, so no design map to share, sorry.
My simple steps:

1. for the right 3 boxes, find the center of center box, drill the first hole there.
2. Mount the longest steel plate on it, and drill the other 2 holes related to it on the other 2 boxes. Angle is not critical, just keep enough nut space inside, before drilling. And mount them.
3. As to these 2 short plates, similar. Notice, make it parallel to the longest one, otherwise, your boxes will going crook.
4. Left 3 boxes, ...
5. mount two group boxes together. I believe you can make it !

The box bottom stl file is the same with original one, nothing changed.