Root Diameter / Interpretation??

[jennin77]

ASME VIII Div.1 Annex 2 / 2-3 (Notation):
Ab = cross‐sectional area of the bolts using the root diameter of the thread or least diameter of unthreaded position, if less

Well, I know it is a detail but I do not find anywhere in the ASME how to calculate the root diameter of a thread.
ASME B1.1 only speaks about "Area at minor diameter" (Table 11) providing a value "for information only" acc.to note 1 and calculated with THE MIN. VALUE OF THE MAJOR DIAMETER WITH MIN-NOTE-3 OF TABLE 2A".
Note 3 : The minimum shown is for unfinished hot material, not including standard fasteners with rolled threads.

It seems more logic to me to consider for ASME VIII Div.1 the Root Area as the area of the minor diameter calculated with nominal dimensions instead to consider this minimum value of the unfinished hot material.

Do you know if ASME provides any rule for that?
I also tried to look at the interpretations but I found only one topic related the the root diameter and not really related to my doubt (VIII-1-86-216).

I have a design where this small difference in diameter makes the difference between verified and not verified....

Thanks

 

[Gr8blu]

Minor Diameter, dm: Also called the root diameter, this is the diameter of an imaginary cylinder (concentric to the thread axis) who's surface touches the thread roots.

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