{HEAD ~ The operation} for coupling {TAIL ~ the metallic parts} 11 and 21 is very simple, as described above 
{ HEAD ~ The operation } for coupling { TAIL ~ the metallic parts } 11 and 21 is very simple , as described above
HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH