I'd like to service a shower valve in a 1957 house with original plumbing.

The bonnet nut uses a round boss 7/8" in diameter with two flats milled
in it about 3/4" apart. It'd be a cinch if the valve stuck out of the wall,
any open-end would fit. Unfortunately it's recessed about an inch behind the
tile, so a socket is reuquired.

All the wrenches I can find fit hex nuts, does anybody know the correct name
for the required tool? From time to time "nuts" like this have crossed my
path, but I've never encountered one used in a position that requires a
socket to grab it.

At this point I don't even know what to look for. Correct terminology would
help a great deal.

Thanks for reading, and any guidance.

bob prohaska