Metz Mecalux 11 slave unit with a rotating flash shoe on top Screw the unit into a tripod thread (1/4in and 3/8in on the base) Or mount it on an accessory shoe. The sensor will then trigger either a gun mounted directly on the hot shoe or a flash connected via a cable using the built in socket.
Old and well used, but still works. The 3/8in socket has been over threaded so a thin layer of plastic cover on the inner wall has broken away. It's not a funtional problem, but just means the interior isn't sealed from dust.