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ＡＰＩ圆螺纹的锥度和中径是两个重要的参数。从理论分析知， 锥度公差和中径公差是相互影响和相互制约的， 目前ＡＰＩＳＴＤ５Ｂ标准中对二者的公差规定未能显示出这种相关性， 因此出现中径公差合格而锥度公差却可能不合格， 以及锥度公差合格而中径公差却超出范围的情况， 这对螺纹公差控制及套管的使用性能带来不良影响。建议将锥度公差和中径公差的控制有效地结合起来， 即变为仅控制中径公差； 也可先确定锥度公差， 然后反推出中径公差的大小， 与紧密距折算的中径公差相比， 精度明显提高。
API thread taper and diameter are two important parameters. From the theoretical analysis, taper tolerance and diameter tolerance are mutually influencing and mutual restraint, the current APISTD5B standards for the two tolerances failed to show that the correlation between the Therefore, the appearance of the diameter tolerance and the taper tolerance may not Qualified, and the tolerance of the taper and the tolerance of the diameter out of the range, which have adverse effects on the thread tolerance control and the service performance of the bushing. It is suggested to effectively combine the control of taper tolerance and diameter tolerance to become only the control of the diameter tolerance. The taper tolerance can also be determined first, and then the diameter tolerance can be deduced, which is comparable to the close tolerance , The accuracy is obviously improved.