The stopper has a first end portion and a second end portion, {HEAD ~ the first end portion} being fixed to {TAIL ~ the cover} 
The stopper has a first end portion and a second end portion , { HEAD ~ the first end portion } being fixed to { TAIL ~ the cover }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL