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