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