snip

Which format? The ones to access two slots on opposite sides of
a retaining ring? Those are what would be called a spanner wrench here
(actually -- "ring spanner") in the US -- unlike the UK where I believe
the term to match what I would call an "open end wrench". The ones
which I have are sets of arms which slide along a bar and are locked to
the bar at the proper distance, and which mount either pins or slot
drivers of appropriate size to match the slots or pin holes.

I actually need both. Most urgently I need the kind which fits into two
slots diametrically opposite each other in the threaded ring. The slots
appear to be square in cross section.

I could also do with having one which fits into a pair of round holes,
too. Like the kind used for "spanner head" screws. But this tool must be
like a screwdriver, as it has to go down the tube of the microscope for
removing the nosepiece.

If you need it, I can photograph my set for an example of a
pretty good set.

If they're no longer available, don't worry. The maker's name might be
useful so I can search on eBay, though.

I also used to have a set from Edmund Scientific which used some
hex steel shaft to hold the arms, with slots milled in them to allow the
arms to cross at a slight angle to the expected right angle. In the
ends of the arms is a hex socket with a setscrew (grub screw?) to hold
them in, and then a pin or slot driver machined on the end. These were
not nearly as rigid, but were quite affordable at the time. I used them
both for camera lenses and for wris****ch back removal/replacement.

Do you know what the official name for the set is?

O.K. Edmund no longer carries anything of the sort, but I have
found an example made in India to the same design. Just better
packaging as it is in a hinged wooden case instead of a cardboard box.
I have not found a price, but perhaps you can with more searching.
Sorry about the extra-long URL

http://anuuj.trustpass.alibaba.com/product/12241451/Spanner_Wrench_Lens_Opening_Tool_Tools_Adjustable. html

Let me break the URL into sections for individual cut-and-paste
if your system does not honor the '' and '' to keep it together:

http://anuuj.trustpass.alibaba.com/product/12241451/
Spanner_Wrench_Lens_Opening_Tool_Tools_Adjustable. html

Unfortunately I can't tell from that picture which tips are included.
It's also too big for my second application.

By the way, this is a ring spanner in the UK:
http://www.britishfasteners.com/mm5/...00003/er14.jpg

Many thanks,

Chris