×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Number of threads pass the nut

Number of threads pass the nut

Number of threads pass the nut

(OP)
Does anyone know a code or a mechanical requirement/justification to have two or more threads pass the nut when torquing hex nuts. I have been told that at lease two threads must show pass the nut and I am not sure why. Please respond. Thanks

RE: Number of threads pass the nut

DIN 78, Bolt End Protrusions, specifies threads extending beyond the nut end.

RE: Number of threads pass the nut

You must have at least one FULL thread showing past the nut, or you will not be sure that there is full thread engagement. If you can count two threads, then even if one is only half a thread (because you can't see the other side) then you can still be certain.

RE: Number of threads pass the nut

Most codes of practice have this requirement for threads projecting past the nut.
This ensures that the full number of threads act in shear when the bolt is in tension, and also ensures that the pattern of stress in the threads at the tip of the bolt is the conventional pattern on which codes and design parameters are based.

RE: Number of threads pass the nut

This requirement is also typical in aerospace, where it also helps to assure that the locking element of "self-locking" nuts (the "norm" in aerospace; typically deformed threads located at the "top" of the nut, etc.) is fully engaged with fully formed bolt threads.  This is also directly related to the fact that many aerospace bolt specifications permit a thread chamfer/point length of two thread pitches.

RE: Number of threads pass the nut

What type of bolts are you using?  The Specification for Structural Joints Using ASTM A325 or A490 Bolts, Section 2.3.2 says "The bolt length used shall be such that the end of the bolt extends beyond or is at least flush with the outer face of the nut when properly installed".  The two thread rule of thumb has been used, but is not required for these bolts.

RE: Number of threads pass the nut

In case of using bolt tensioner, two threads are not enough.

RE: Number of threads pass the nut

Two threads was probably asked by the design
guys to ensure because of stack up of tolerances
that the flush or extended case would exist.
You cannot design flush conditions unless every
thing is perfect and we are not there yet.

RE: Number of threads pass the nut

One of the good things about this practice is that as a supervisor it is one of those quick visual inspections you can do on a bolted joint to ensure it is OK.  If you see negative thread protusion and/or excessive protrusion you investigate because you either have a tradesperson who does not know their trade or who does not care.

RE: Number of threads pass the nut

I have stayed out of this thread until now because the original question has been fairly answered, but---As a good supervisor one should know the capabilities of his people.  If they don't know their trade either teach them or replace them.  If they don't care, turn them into 'cash'!
As to the one thread, two thread question--- in the heavy construction industry we have come from two thread (the accepted 'norm' of 30 years ago) projection to 'flush nut', the common practice in the L.A. area for the last few years.  With the now common practice of using TS bolts, the problem of overtorque has largely been solved (along with the noise problem).  In my practice with auto and aircraft restoration/racing, where safety wireing is not required, Nylocks work quite well at 'flush nut'.

Rod

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources