I'm wondering about this for a while.
How much thread is required to be engaged to get "quote" full strength from a fastener i.e. nut or threaded rod etc...?
I always went by the width of the bolt that's how deep it would need to be anything under and it could strip anything over was not really required? I have heard anything from 4 threads to 1.5 x the width of the bolt, is there a standard or formula for this.
I am thinking a straight push and pull as far has thread engagment not any kind of side load.
thanks

My grandfather who was a Mechanical Engineer told me that 3 threads is minimum for full strength.

Eric

If I remember correctly from my basic physics junk (its been a while, I'm a theoretical physics junkie, this real world crap I usually get messed up on) the threads are the length of a lever arm wrapped around a pillar, so the more thread engagement, the stronger the fastener will be in tension. I always heard 1.5 * Diameter was the way to go. Sheer is a different story though.

1.5 x dia. is considered "standard" ....


:usa:

When specing blind tapped holes at work (and the fasteners to go with them), generally shoot for 1-1.5 times the diameter of the fastener, and make sure the threads are 2 times the diameter deep.

Pete

3 threads I just got my laugh for the day.
actualy grampa probubly did not work
whith fine threads.

1.25xdiameter will do.

1 x diameter is not used as usualy the
first half of a thread on a bolt is
not a complete thread. it is more of
a starter thread.

if you look at most bolts(not all)
they are generaly 1.25 x diameter of the
threads overall dim

Thanks for the answers.
Looking at my orig post I meant to say 1.5 x dia of the bolt I think I'll stick with that it just sounds right :)
Again thanks...

3 threads I just got my laugh for the day.

Then you clearly do not have a good understanding of how threaded fasteners work.

Grandpa was right....full strength can be achiedved with just 3 full threads..in fact, the vast majority of the load is borne by the first thread, and exponentially less as you go. 1.5 x dia. is recommended to give you a design factor (sometimes erroneously called a safety factor) as well as to alleviate potential problems from loosening of the threaded assembly.

So - theoretically speaking - 3 is good

practically - use 1.5 x diameter.

If you wish to know more - recommend you read "High performance hardware" by Forbes Aid. One of the best books you'll ever read