Hi JP, I had a similar issue with genbox when I wanted to create a simple mesh where periodic BCs are shared between different boxes. I haven't tested Paul's suggestion yet but I wrote a genbox inspired python script that did the job in my case. You can find it here: https://github.com/Steffen1989/code-snippets (genbox.py) The Input is very similar to genbox but you can specify a periodic BC shared between two boxes with P01, a second one with P02, ... and the same with internal BCs, i.e. E01, E02, ... This can create a 2d mesh, which is afterwards extruded with n2to3 in the third direction. Note that it has not been tested thoroughly but you are welcome to give it a try and contact me if you run into troubles. \Steffen