Mk7 Stores Ref: 6D/2854 | Drawing No: MX2468-266C
The Mk7 PEC was only used in the RAF for Vulcan B2 and Victor K2 rear crew.
A "Swivel Seat Type" PEC for low altitude, it provided connections for: breathing oxygen, bail-out oxygen cylinder, and communications.
The Mk7 PEC was replaced by the Mk 11 when modificatin MX98 was introduced, changing the ML Aviation quick release coupling to the aircraft hose, as explained in the quote below.
Note: This PEC is commonly know as an "SSC", or Swivel Seat Conenctor, but this term is absent from documentation I've found so far.
Quote:
The oxygen mask hose assembly Mk 11 is a low altitude assembly used by rear crew members of Vulcan and Victor aircraft. It is designed to replace the oxygen mask hose assembly Mk 7 by the embodiment of Modification MX98 which introduced the personal hose assembly coupling Mk 2 in lieu of the quick release oxygen connector. The assembly permits high altitude bail-out without loss of the pressure breathing facility from the emergency oxygen system.
This image shows the Mk7 PEC.