This modular spice rack is set up to friction fit together for stacking.

They are attached horizontally with pins that should also friction fit. I did have a couple pins that ended up more loose than expected. In that instance a drop of super glue was used to hold them in place.

2020-09-06: Added a hook that will hold light items on the side of the rack. It will friction fit, but a couple drops of super glue should be used to keep it in place. The photo shows the pasta gauge at https://www.thingiverse.com/thing:3894895 hanging from the hook.