{HEAD ~ The external corner formative member} 1, wherein {TAIL ~ the angled corner plate portion} is formed flush with the front plate of each of said groove portions 
wherein
{ HEAD ~ The external corner formative member } 1 , wherein { TAIL ~ the angled corner plate portion } is formed flush with the front plate of each of said groove portions
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH