api 5000API has specified weld necks for many 6BX flanges, and not done so for many others, but API has provided the basis for determining the dimensions of a 6BX integral flangeBeware, some suppliers and manufacturers supply normal A105N 36K material flanges stamped as 3,000 or 5,000, these interconnect with API sizes (example a 2 ANSI A105 1500 class flange rated at 3,700 psi CWP is the same as