| 摘要 |
A drill string comprising first and second drill members which are threadedly engaged with each other. Each drill string member has an elongated body and a helical thread on the elongated body. The thread may be roll formed. The helical thread has a helical root portion, a helical crest portion and flank portions interposed between the root portion and the crest portion. The helical crest portion has a maximum radial projection adjacent the flank portions. The helical crest portion has a recess with the maximum depth thereof preferably disposed generally midway between the lateral extremities of the crest portion. The recess may be generally Vshaped and has a maximum depth of about 0.003 to 0.030 inch. In one embodiment, the sidewalls define an angle of about 2 to 20 degrees with respect to a plane passing transversely through the lateral edges of the crest. |
