In article ,
says...

I'm impressed. In some other groups I've been asking about a
one-piece stereo to mono headphone adapter. I want one with a
built-in switch but even though it's not available I don't think
I'll be doing that to fit one!

http://al.howardknight.net/msgid.cgi?ID=148001642200

If, as in link, it has a mono socket, what is the "mono/stereo" switch
going to do?

Mike.