In my experience, U.S. clothes dryers don't use
twist-lock plugs. So
I'd expect them to use a NEMA 6-20R or 6-30R non-locking receptacle.
I have never seen a clothes dryer with a twist lock (but they may be out
there).
For anyone interested in big machines from the 1980s and 90s, L6-30 is a
*very* common plug and socket combination, so salvage them whenever you
can - they are not cheap. I saved quite a few when I was deinstalling the
old NSFnet RS/6000-T3Bs. I am glad I did.
William Donzelli
aw288(a)osfn.org