API casing thread gauging

[ngauge]

Please advise what specification is used to manufacture the thread gauges go and nogo for the following:

6" api 6a back pressure valve threads HBPV
Atlas Bradford gauges and the like.

thanks much....

 

[Hush]

These are proprietary threads so the correct answer is:
The standard for the H BPV gauge is owned by Cooper Cameron and the standard for the Atlas Bradford gauge is owned by Grant Prideco.