| 摘要 |
A tool for drilling a cylindrical hole with an enlarged end undercut portion comprises a shank with cutting edges and a drill collet screwed to the shank by a knuckle thread. The collet is provided with a stop collar having a semispherically-shaped face supported in a matingly configurated recess provided in a stop plate so as to form a swivel bearing. A portion of the collet is closed by a bell connected to the stop plate and formed with a central hole to receive the shank of the tool.
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