| 摘要 |
In a die for forging a metal tube to form a semi-product of a unitary combination nipple, a die body has annular first, second and third inner surfaces, and a die cavity. The die cavity includes a large-diameter outer cavity portion with a uniform diameter defined by the first inner surface and adapted to permit insertion of the tube into the die cavity therethrough, a small-diameter inner cavity portion with a uniform diameter smaller than that of the outer cavity portion and defined by the second inner surface, and a polygonal cavity portion disposed between the outer and inner cavity portions and defined by the third inner surface. The second inner surface is located inside the first inner surface, and the third inner surface is located inside the first inner surface but outside the second inner surface.
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