| 摘要 |
The shank (1), e.g, for a drill, thread cutter or milling bit, has a base (2) which is preferably cylindrical in shape, with three flat faces (4,5,6) lying parallel to its axis of rotation. One of the flat faces has a recessed portion (4a) which lies nearer to the axis of the shank than the other three. The edges of the flat faces meet the surface of the base to form alternating cylindrical and flat surfaces, and the base also has an annular groove (10) to fix the instrument from axial movement.
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