| 摘要 |
An improved roof drill bit and roof drill driving assembly which is characterized as a "hands off" type in which the drill, driver, and drill extension are designed and assembled to have a stability which enables the operator to avoid guiding the drill with his hands. An improved drill bit prevents plugging of the assembly when used with suction systems and provides a heavier wall construction. Special adaptors are provided for driving drills and drill extensions.
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