We assume that your concern involves only 6BX connectors, as most wellhead manufacturers currently do not make 6B connectors, either open face flange or studded face flange, with raised faces.

API does control the raised face dimension on 6BX connectors, but not within limits that will allow interchangeable tap end studs in studded face flange connectors.

WOODCO USA and most other manufacturers design studded face connectors without a raised face as permitted by API Spec 6A. No raised face on studded face connectors permits defacto standardization of tap end studs.

Note that the face to face make-up design of 6BX connections requires that at least one face of the two mating connectors has a raised face. This has resulted in a standard practice of always having a raised face on 6BX open face flanges, and a defacto standard of always omitting the raised face on studded face flange connectors (Some rare exceptions exist, e.g. NOVShaffer uses maximum height raised faces on studded face connected blowout preventers).

Some persons do not know of this defacto standard, or that API Spec 6A permits a studded face 6BX connector with raised face omitted: see API Spec 6A, 19th Edition, page 250, note b. "Q" may be omitted on studded flanges."

In 1995 AWHEM formed a Task Group to specify interchangeable flange bolts and tap end studs for API Spec 6A open face flanges and studded face flanges. You can view the resulting document at: http://www.awhem.org/PDFs/TR9501A.pdf .

WOODCO USA provides Web Site Tools for identification, estimating, and reference only. Do not use this information for manufacturing or inspection. Users of these tools should not use them as a substitute for professional engineering advice.  Anyone making use of the information presented does so at his own risk and assumes any and all liability resulting from such use.