| 摘要 |
A cutter shell for cutting a circular opening in a metal object formed of a unitary metallic member having a tubular boring portion and an inverted dish shaped head portion. The boring portion has a tubular sidewall and teeth at the forward circumferential end. The sidewall is of thickness not greater than the teeth. The head portion has an outer circumferential perimeter secured to the tubular portion rearward circumferential end. The head portion has an inner concave surface as viewed through the tubular boring portion and an outer convex surface. The thickness of the head portion is not substantially greater than that of the boring portion tubular sidewall so that the head portion deflects inwardly in response to boring pressure, the deflection being radially transferred to the boring portion tubular sidewall to stiffen the sidewall and hold it in more perfect circularity during boring action.
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