one planar portion matched to one of {HEAD ~ said flat portions} of {TAIL ~ said elongated mating member}, 
of
one planar portion matched to one of { HEAD ~ said flat portions } of { TAIL ~ said elongated mating member } ,
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH