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       2、      With the same specifications for the different types of thread portfolio, portfolio collar.

       3、      Appendix A8 (SR13) to seal ring groove, the seal ring to the collar.

       4、      Non-upset and extend-upset tubing use special-bevel couplings

                  1、  Tubing thread casing  4〞 4¹/₂〞 non-upset tubing 、extend-upset 

                           teeth/inch, but the diameter of couplings boring are different。

                  2、  Tubing round thread casing  coupling high gear  8teeth/in=1.81mm 

                          10 teeth/in = 1.41mm

                  3、  Buttress thread casing high gear 5teeth/in=1.57mm

                  4、  Casing round thread casing coupling high gear 8 teeth/in=1.81mm