api5000API 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 flange that the manufacturer may attach to aAPI 5000 (Class 1500) Connection Types Performance Requirement API 6A Flange Means; Studded; Bolted; PR1; PR2; American Petroleum Institute; Coating Types Of API STD 6A Hh