I think the lower 'hinge' is just a thicker part of the ring
that makes contact with the plate on the door
(
Mockingbird Practitioner of SCIENCE,
Tue 20 May 2008, 13:51,
archived)
*FWAPS*
(
Wobbly Bloke Hello, did I miss anything on,
Tue 20 May 2008, 13:59,
archived)