Why is there no Series II in the new GB/T 12459-2025?
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As the title suggests, the new version of GB/T 12459-2025 does not include Series II； If pipes from Series II are chosen, how should the fittings be selected?
It can be selected; clause 6.1.2 of GB/T 12459-2025 specifies that the nominal size, outer diameter at the ends, and nominal wall thickness of the pipe fittings shall comply with the provisions of GB/T28708 and Appendix B. The outer diameters at the ends of the fittings are divided into two series: I and II. The outer diameters listed in the size tables for each fitting correspond to the standard I series diameters, which are the recommended choice. The outer diameters of the II series are not standard, and when using this series, it is necessary to indicate “-II”.