| 摘要 |
A roller cutter (28) of a drill bit (10) is retained on a journal (24) for rotation by a retainer ring (82) having external screw threads (88) which are threaded onto mating screw threads (108) on the roller cutter (28) for rotation therewith. The retainer ring (82) is mounted within a semicircular groove (68) on the journal (24) and has an inner periphery formed of a smooth arcuate surface contacting the annular groove at a position spaced at least 10 DEG from the entrance opening of the groove thereby to reduce bending stresses exerted against the root (74) of the groove (68).
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