| 摘要 |
A downhole drill bit having an elongated male drive shank, a separate female impact head mounted on the drive shank, the drive shank and head having cooperating external and internal, head drive splines extending helically in one angular direction to urge the drive shank and head together during impact drilling, the head drive splines having a width and spacing for inserting and then rotating the head on the shank, and elongated key inserts between the head drive splines to form therewith a head drive coupling, the head having an annulus and the drive shank having a circular arrangement of locking lugs receivable within the annulus for locking the head against axial withdrawal from the shank.
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