a receiving portion which has {HEAD ~ a space} for pulling in {TAIL ~ the second end portion} of the stopper 
for pulling in
a receiving portion which has { HEAD ~ a space } for pulling in { TAIL ~ the second end portion } of the stopper
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH