Therefore, in order to sustain impact upon hammering, it is effective that the screw is formed so that the outer diameter of the smaller diameter parallel thread part 15 is equal to or smaller than {HEAD ~ 1.8 mm} for {TAIL ~ the C type steel plate structural material} having the thickness of 0.5 mm or 0.8 mm 
for
Therefore , in order to sustain impact upon hammering , it is effective that the screw is formed so that the outer diameter of the smaller diameter parallel thread part 15 is equal to or smaller than { HEAD ~ 1.8 mm } for { TAIL ~ the C type steel plate structural material } having the thickness of 0.5 mm or 0.8 mm
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