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