| 摘要 |
A roof bolt bit arrangement comprising a combination spade drill body having a rotational axis, a shank portion, a generally planar spade cutter portion with a pair of oppositely directed cutting edges extending radially of the axis, and at least one rotatable frusto conical cutter mounted on the shank portion with its cutting edge in the path of the maximum radial extent of each spade cutter portion cutting edge.
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