a biasing member adapted to apply {HEAD ~ force} to the stopper for pulling in {TAIL ~ the stopper} into the receiving portion; and 
a biasing member adapted to apply { HEAD ~ force } to the stopper for pulling in { TAIL ~ the stopper } into the receiving portion ; and
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH