Here's some photos of a pipe a picked up a while back. It's unique and I think its a bit gimmicky. Back when the pipe was made there was a sort of "Arms Race" involving stingers and inserts that were all promising the ever elusive "Perfect Smoke". In the case of this Underboar its a combination of stinger and cleaning aid. In its former life this pipe was smoked very hard and then put away dirty (very typical for that age of smoking). Here are the pics. The two diagrams I shamelessly lifted from Pipephil.EU.