api5000API 6A Type 6B 5000 PSI Weld Neck Flanges are generally used in hh pressure applications, where hot or cold temperatures exist. These steel API 6A weld neck flangesAPI 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 a