In his email he said this:
So the rings are not the original ones, but they would be of a similar type and size. But I asked Andrew a bit more about the organiser and he confirmed that the back cover is wider than the front cover, which confirms his thoughts about it being able to be clipped on to the rings of a larger organiser.I discovered your excellent blog last year when I was looking for somewhere to mend my grandfather's filofax. The metal spine and ring binders had become detached from the cover. In the end, I had to find a second hand filofax with as small rings (still a bit bigger than the original) as possible and the repairers took them out and put them into my cover.The filofax was used by my grandfather who had a chemist's shop in Surrey. My 80 year old mother says she remembers him using the filofax when she was a girl so it must date from the1930s or 40s. It's black leather and has 6 holes along the side of the slightly larger back cover so it can be inserted into larger (desk) filofax. I couldn't find it on any of your catalogues or in the pictures of vintage filofaxes. I use it as my holiday organiser.
It would therefore fit a Personal Duplex (two sets of rings) type organiser like those shown here It would fit a large ring ordinary personal size as well but may be it would add too much bulk?
Andrew mentions in his email above it fitting a Deskfax, whilst this is true (the ring spacing is correct) the Deskfax didn't appear until 1993!
It's not shown in the old catalogue I have from about 1937. Thank you Andrew for sharing this with us.
Have you ever come across anything like this before?