{HEAD ~ another planar portion} continuously formed with said arcuate portions and matched to {TAIL ~ the other flat portion} of said elongated mating member, 
{ HEAD ~ another planar portion } continuously formed with said arcuate portions and matched to { TAIL ~ the other flat portion } of said elongated mating member ,
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH