{TAIL ~ The locking mechanism} 7, wherein the predefined angle is {HEAD ~ 180°} so that the first and second sets are opposite each other 
{ TAIL ~ The locking mechanism } 7 , wherein the predefined angle is { HEAD ~ 180 ° } so that the first and second sets are opposite each other
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH