| 摘要 |
A one or two-piece rotary drill includes a steel shank adapted to fit into a chuck of an electric drill, a drill bit and a frusto conical or frusto spherical file between the shank and the drill bit and all of which are disposed on a common longitudinal axis. The frusto conical or frusto spherical file includes a plurality of crowned teeth about its periphery and wherein each of the teeth have a front cutting side and a back side which includes a plurality of sharp serrations thereon. The composition of the steel tool includes carbon, silicon, molybdenum and chrome. A rotary tool set including a plurality of drill bits and file portions having a plurality of shapes is also disclosed.
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