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