The french circuit breakers have a very standardised format. I wanted to measure the actual parts but it's better to read the books and I found some informations. Crucially: the module widths are multiples of 18mm.
I had to measure something anyway : the inputs are 4mm wide so the PCB's teeth should be around 3.5mm wide.
There must also be some room for a copper busbar, probably behind the PCB.