| 摘要 |
A threaded joint for coupling two drill rod elements includes a first drill rod element having at least one end thereof a male tapered helical threading with a cone opening angle greater than 1 DEG and less than 3 DEG . The threading has a constant pitch determining an angle of inclination of the decreasing helix as greater than 1 DEG and less than 3 DEG at the beginning of the helical threading. A second drill rod element has corresponding female tapered helical threading. Each tapered helical threading has primary and secondary shoulders on opposite ends thereof and a stand-off between the primary shoulders when the male and female tapered helical threading are manually fitted together. The male tapered helical threading has discharge grooves in an unthreaded zone for deflection of lines of force. The primary and secondary shoulders have a truncated cone shape, and the ratio between the cone opening angle and the angle of inclination of the helix at the beginning of the tapered helical threading is less than 2.
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