On Thu, 20 Aug 2020 12:44:58 -0700 (PDT), jkn
wrote:

snip

Well, my assumption (correct I *think*) is that they are a standard size - as I say,

Ok ...

I am taking it to be a
modular system with some commonality.

Well, you often get several competing systems and then others come
along that share one of the designs and hopefully (at some time) they
all default to the same format. ;-)

'Sorta-case' seems to be the generic form. I've seen a list of dimensions:

Yes, I've seen many of that sort of thing, never assumed (or checked)
if they were a generic size / format etc.

45mm, 63mm & 83mm Deep
54 x 54 mm Orange
54 x 108mm Yellow
108 x 108mm Blue
54 x 216mm Green
108 x 162mm Green
108 x 216mm Red

If my assumption turns out to be incorrect, then yes, I do have a backup path involving 3mm MDF
and hot-melt glue. But I suspect there are (removeable) alternatives to that, hence the Question:...

I was thinking of (you) *making* such boxes from hardboard / MDF, not
just making the dividers?

If you were able to optimise on one or two sizes, you (I) could 3d
print a construction frame. You cut the panels and drop them into the
frame (like glass in a fish tank) then run hot-melt-glue round the
inside, cool, rinse/repeat. ;-)

Cheers, T i m