An engagement occurs between {TAIL ~ the first and second elements} in the closed condition of {HEAD ~ the abutment structure} 
An engagement occurs between { TAIL ~ the first and second elements } in the closed condition of { HEAD ~ the abutment structure }
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD