Such apparatus may be used to machine internal and external surfaces of a polygonal or other non circular contour, and is especially suitable for the machining dies used in the casting of hexagonal bolt heads, {HEAD ~ more particularly domed bolt heads} wherein {TAIL ~ a hexagonal rim} merges into the domed surface of the head 
wherein
Such apparatus may be used to machine internal and external surfaces of a polygonal or other non circular contour , and is especially suitable for the machining dies used in the casting of hexagonal bolt heads , { HEAD ~ more particularly domed bolt heads } wherein { TAIL ~ a hexagonal rim } merges into the domed surface of the head
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