which is stronger

Jeff B

Jeff B

Thanos was right
Joined
Dec 23, 2006
Location
Lincolnton N.C.
Had a discussion with a friend at work about this.

Which is stronger on a bolt & nut inside thread or outside thread?

My bolt vendor says inside. I believe this. I.v found when I over torque a bolt normally the bolt will break or strip the threads before the nut (inside threads) give.

What do you guys think??
 
To add to it, you also have rolled vs. cut threads. I remember reading somewhere that while it is possible to roll an internal thread, it is nearly never done.
 
Id say it all depends on the way that the threads were cut, as well as the quality/strength of the material... a grade 8 bolt or nut will strip out a grade 5 no matter which one is the 5... if both pieces are identical, then i have no clue as to what would break... typically you see the bolt fail, but that has alot to do with how the torque is applied through the 2 pieces and the high area of stress concentration at the head of a bolt.... I have seen a nut bust apart though from too much torque, so....
 
Im gonna go with the nut (internal thread). Though the amount of surface area is the same on the thread faces, the thicker part is at the larger diameter on the nut, which leads to a greater overall cross section. While the difference is very small (some function of roughly 1/3 the depth of the thread, the diameter, and the thickness) it should be enough to tear up the bolt first.
 
I'll say the nut is stronger, but not neccessarily because of the inside threads.
The force on a nut is spread out around the entire nut.
A bolt usually breaks right before entering the nut, where all of the stretching force in concentrated.


Matt
 
I too have to say the nut. I have broke many bolts off but I myself have never busted a nut( that sounds funny!) Case in point, reusing ubolts and also once with new ubolts, I stripped off the threads of the bolt.

Good question though
 
The internal thread is inherintly stronger.
The contact patch of the internal thread is imbedded into the surrounding supporting material.
here a the contact patch on the external thread is elevated above it's support material.

Although this has nothing to do with bolts breaking vs. getting nuts off (or the inability there to:fuck-you: )it is about destroying the threads on one vs another.

BTW try the grade 8 bolt into a grade 5 nut sometime, you might be surprised ;)
 
My dad has been in the Fastner Industry for about 30+ years.

I asked him so I could relay the info. Here you go:

To say that either an internal or external screw thread is stronger than the other is a misconception if you are stripping threads or breaking bolts you have pushed them beyond their physical limits. There are to many contributing factors to be considered a simple example is if you screw a grade 2 nut onto a grade 8 bolt obviously the nut will strip before the bolt fails reverse is and the bolt will fail before the nut. Quoting right out of the 7th Edition of the Inch Fastener Standards of the Industrial Fastener Institute under the heading Bolt Failure is the Preferred Failure Mode it reads "In selecting fasteners, designers should strive to assure that if a failure should occur--- from overtightening during installation or overloading in service---- that it be bolt fracture and not thread stripping" that means that the engineers design it that way which would cause most people think that nuts are stronger, all things being equal the "threads" are the same strength, but since the strength of a nut is measured across the flats (wrench size) and the strength of bolt is measured across the shank of the bolt a nut of the same material is the stronger element of the joint.

Do you want me to fax you about 100 pages of the IFI "Basic Elements of Screw Thread Design" it will tell you more about screw threads than you really ever wanted to know or you can go to www.askdadaboutboltsandnuts.com....................
 
mbalbritton said:
My dad has been in the Fastner Industry for about 30+ years.

I asked him so I could relay the info. Here you go:

To say that either an internal or external screw thread is stronger than the other is a misconception if you are stripping threads or breaking bolts you have pushed them beyond their physical limits. There are to many contributing factors to be considered a simple example is if you screw a grade 2 nut onto a grade 8 bolt obviously the nut will strip before the bolt fails reverse is and the bolt will fail before the nut. Quoting right out of the 7th Edition of the Inch Fastener Standards of the Industrial Fastener Institute under the heading Bolt Failure is the Preferred Failure Mode it reads "In selecting fasteners, designers should strive to assure that if a failure should occur--- from overtightening during installation or overloading in service---- that it be bolt fracture and not thread stripping" that means that the engineers design it that way which would cause most people think that nuts are stronger, all things being equal the "threads" are the same strength, but since the strength of a nut is measured across the flats (wrench size) and the strength of bolt is measured across the shank of the bolt a nut of the same material is the stronger element of the joint.

Do you want me to fax you about 100 pages of the IFI "Basic Elements of Screw Thread Design" it will tell you more about screw threads than you really ever wanted to know or you can go to www.askdadaboutboltsandnuts.com....................
Click to expand...
Now thats alot of good info??
 
Back
Top