Quad 33/303/FM3/405 and others -  mains power cable for kit which uses the mini Bulgin plug.

Electrically safe mains power cable for connection of the Quad 33 Control Unit, FM3 tuner or 303 power amplifier (originally the 303 is earthed via the 4 pin interconnect which is why the Quad system used 2 core cables from the 33 to the 303).