David Clark H10-30 (2) & H10-40 Pilot Aviation Headset Headphones Dual Plug.  One of the H10-30's has a single plug and could not be tested for sound (and does not have a mic).  The other H10-30 and the H10-40 were tested for sound.  The single plug H10-30 and the H10-40 both have volume control knobs.  These came from the estate of a well known local pilot.