RAACO Assorter 55 boxes are excellent and are my preferred storage for small parts. I was a bit space limited and wanted to fit more boxes into the space where six handy-box frames fitted previously so I made these double side mount pieces. When attached to a suitable frame you can fit as many assorters as you like. 

(In the photo the catch on my “Electro 22, 33” box was not closed properly. I have fixed it.)