Grimly Curmudgeon wrote:

I see what you're getting at, but the pattress has always been just the
wooden plate and the term 'pattress box' refers only to the surface box
that would screw onto it.

There was an intermediate step between the wooden pattress and the
modern surface mounting box.

Originally wiring accessories for surface mounting had terminals open at
the back and were screwed to the wooden pattress. When the wiring regs
introduced the requirement for all connections to be enclosed in
fireproof material (12th or 13th edition?) many manufacturers introduced
moulded mounting plates (aka back plates or pattresses) that could be
used either on a wooden pattress or directly on a wall. Thus the wooden
pattress started to disappear. The next step was the introduction of
the surface mounting box as we now know it, enabling 'flush-mount'
wiring accessories to be surface mounted.

I guess this is how common use of the term pattress passed from the
wooden item to the surface mounting (pattress) box. There's no such
continuity with flush mount wiring accessories and their metal back
boxes, which were in use before the wooden pattress disappeared. That's
why using pattress to refer to flush mounting boxes only confuses the
issue and is quite wrong, IMHO.

--
Andy