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