I am struggling with the ASME B16.5 code and the specified stud-bolt length that is taken into account in the tables (7, 10, 13, 15, 17, 19 and 21).

If you calculate the stud-bolt length according the "guidelines for stud-bolt calculation" for a NPS 24 Class 150 welding neck flange, the stud-bolt length should be 7.45in.

When I look in the ASME B16.5 Table7 the length is 6.75in this is 0.7in difference with the ASME B16.5.

Studbolt length image

What are the required number of free threads? As far as I am aware from bolt size 1in and up the number of threads per inch is the same and size S is fixed. If you keep calculating with S = 1/3 bolt diameter the number of free threads will only increase with no use?

  • $\begingroup$ As engineering practician, I'm not depends on studbolt length advised by ASME B16.5. We use our own studbolt length table (based on experience) which we see better. That's what I recommends. $\endgroup$
    – RainerJ
    Sep 11, 2017 at 11:15
  • $\begingroup$ Do you find that the length is generally too short in the ASME table? $\endgroup$ Sep 13, 2017 at 6:21
  • $\begingroup$ Do you find that the length is generally too short in the ASME table? Yes, some bolts are too short but others are ok. $\endgroup$
    – RainerJ
    Jul 21, 2021 at 1:13

1 Answer 1


In small bolts, threads is 1D but in larger size is less than 1D. Free threads in best practice is 2-3 threads. Don't forget to take gasket thickness (SPWD or RTJ?) in calc.

Additional free threads of 1D may be required if hydraulic tension fastening method to be used. Hydraulic puller will need enough (1D) thread engagement to pull the studbolt.


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