Exactly! The whole assembly is flush with the cockpit sole. The
cover is male, threads into the frame. Nothing to grab onto at all,
except the two little holes (1/4" deep) for the spanner. I've thought
of drilling the cover so I could get a good grip on it but then I
would have a cover with holes in it, and I don't know where I could
ever get a replacement (it's 1976 vintage) -MG

If the emergency rudder cover plate is anything like the smooth, flat one on
the Mirage 33 I sail on, this tool may not be able to grip the edges.