{HEAD ~ Each groove portion} 12 is constituted by a front plate portion 14, {TAIL ~ a bottom plate portion} 15 and a back plate portion 16 
is constituted by
{ HEAD ~ Each groove portion } 12 is constituted by a front plate portion 14 , { TAIL ~ a bottom plate portion } 15 and a back plate portion 16
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH