Christopher Tidy writes:

What's the official name for these spanners?

Spanner wrench or adjustable spanner wrench. The first fixed type is a
thin hollow tube with tiny projections on the end to fit the holes or
slots in the retaining ring. This is better at deeply recessed
locations. The second is the adjustable gadget with interchangeable
tips.

See: http://www.thorlabs.com/advSearch.cfm and search for "spanner".

See: http://www.edmundoptics.com/ and search likewise.

I'm reluctant to try it. I don't want to cause any damage.

Really, just nudge it with a jeweler's screwdriver or dental pick and
see if it doesn't back right out.