I was thinking valves originally. I'm pretty sure this the "rim" around e.g. hose or pipe connectors.

You also get "insteekflensen".

The "steekflens" could best be described as the seating for a seal.

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Note added at 2004-07-05 14:29:56 (GMT)
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This might be of use Chris.

http://www.globalsecurity.org/military/library/policy/army/f...

Flange

A protruding rim, edge, rib, or collar, as on a wheel or pipeshaft, used to strengthen an object, hold it in place, or attach it to another object.