| 摘要 |
The structure has a drill tip (21) of a cutting part and a drill body (22) with two radially reverse screw slots, where the body has an extended clamp. A blade end (24) is installed at an outer side of a scrape surface (23), where a bottom of the scrape surface and an end of the drill body forms a reverse hook. A scrap-release slope (25) is installed in between the scrape surface and the drill tip.
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