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