How do I test unknown bolts?

[Batmanacw]

Lots of good info here. But let me add a few important ones.

Testing to failure is a great way to test the final strength of a bolt. But then the bolt has been ruined.

Testing a sample of Bolts to failure is not a valid test unless all the Bolts and their histories are identical. Yours are not.

Therefore testing to failure isn't very useful.

You can certainly test to recommended torque for that size and grade. This won't have any affect on a good bolt. However, this does not in any way evaluate the strength of the bolt. Recommended torque is the torque required to hold a bolt in the fastened state under load. It is not intended to permanently deform the threads. Design torque maintains the stresses well inside the elastic range - well below the point where they deform or stretch permanently.


My advice is to use them as is. If they take their design torque they will likely be just fine. The only exception would be bolts that have started to fail in fatigue. But there is no way to test for that in a home shop. For mission critical applications, go get new bolts.

I would not use the grade 2 bolts in high stress applications, but for $20 I could not pass on close to 150# of decent bolts.

Half the bolts I own are grade 8 (12.9) cap screws of various types along with a substantial amount of grade 5 and some grade 8 bolts.

Unfortunately I'll still be buying bolts at hardware store prices for some applications.

 

[sdelivery]

Please don't take offense, I am not a bolt snob or anything. I don't buy anything but grade 8 and I don't keep around upgraded hardware but with a few exceptions.
I can only afford and store one "bolt house" I need to be able to count on any of the fasteners to do its job.

 

[Batmanacw]

Please don't take offense, I am not a bolt snob or anything. I don't buy anything but grade 8 and I don't keep around upgraded hardware but with a few exceptions.
I can only afford and store one "bolt house" I need to be able to count on any of the fasteners to do its job.

The bolts are not ungraded. All bolts are graded unless they existed before the current grading system.

 

[Susquatch]

Please don't take offense, I am not a bolt snob or anything. I don't buy anything but grade 8 and I don't keep around upgraded hardware but with a few exceptions.
I can only afford and store one "bolt house" I need to be able to count on any of the fasteners to do its job.

You have an interesting outlook on Bolts. I do the same as you except that my "bolt house" (to use your words) is full of standard Bolts, not grade 8. There are many situations where a grade 8 bolt is not a good idea and vice versa. For example, a grade 8 bolt in a threaded hole into regular strength steel would fail the hole before the bolt which is generally not the preferred failure mode. Grade 8 Bolts are best used in combination with grade 8 nuts not threaded holes. Most users forget that properly used Bolts stretch when torqued down. It is this stretching which creates a proper joint and that also dictates the proper torque. To stretch properly, grade 8 Bolts require more torque. But more torque is not always good for the parent joint. Then there is cost and availability. It's much more cost effective to maintain a house of standard Bolts than grade 8 and only buy grade 5 or 8 as needed.

Let's not forget about shear applications. I cannot begin to describe the cost implications of using grade 8 or regular grade Bolts in a shear application. The damage done can be many thousands of dollars making the cost of the bolt insignificant. Yet I see it all the time.

The bottom line is that it is important to use the right fastener for the situation and to use it correctly.

 

[sdelivery]

You have an interesting outlook on Bolts. I do the same as you except that my "bolt house" (to use your words) is full of standard Bolts, not grade 8. There are many situations where a grade 8 bolt is not a good idea and vice versa. For example, a grade 8 bolt in a threaded hole into regular strength steel would fail the hole before the bolt which is generally not the preferred failure mode. Grade 8 Bolts are best used in combination with grade 8 nuts not threaded holes. Most users forget that properly used Bolts stretch when torqued down. It is this stretching which creates a proper joint and that also dictates the proper torque. To stretch properly, grade 8 Bolts require more torque. But more torque is not always good for the parent joint. Then there is cost and availability. It's much more cost effective to maintain a house of standard Bolts than grade 8 and only buy grade 5 or 8 as needed.

Let's not forget about shear applications. I cannot begin to describe the cost implications of using grade 8 or regular grade Bolts in a shear application. The damage done can be many thousands of dollars making the cost of the bolt insignificant. Yet I see it all the time.

The bottom line is that it is important to use the right fastener for the situation and to use it correctly.

Hahaha, that reminds me of tightening me bhcs's into a Chinese made bed with the short side of an Allen wrench and tearing the threads out!
Good argument but it's not reality.
I remove dozens of damaged fasteners each year and the sheared fasteners are the easiest to remove.
If the casting/housing threads pull out there is a helicoil in the future.
I scrap all the lo grade stuff.

 

[tq60]

Most of what we do does not need higher grade stuff.

Even at the wholesaler the higher grade is much more expensive.

Most of our hardware is from lifetime of "finding", stainless from cell sites as tower crews drop lots, buckets of assortedfrom estate sales, one a farm with a wall of stuff to the sometime just buy them.

When we need the high grade we buy them, but for general stuff the cost sometimes just is not justified.

Yes, we are cheap, hard to justify a grade 8 1/4 20 bolt to hold a sheet metal (aluminum) into a threaded hole in relay rack.

Correct materials can save money better spent on other parts of the project.

We did buy only the grade 8 stuff for a short time as we were having some failures with some equipment.

But other stuff would fail instead which would be harder to fix, when the lower grade would fail it would give indication of failure, replace the bolt and tighten rest, inspect while there.

The higher grade would no longer be the weak link, now the thing that would cause the stress on the pert now instead of breaking a bolt now break the bracket the bolt is attached too.

Like putting a bolt into a fuse holder.

This is dependent on the specific circumstance, just something for consideration.

Sent from my SM-G781V using Tapatalk

 

[matthewsx]

The fastener is usually the least expensive part of the assembly. I use plenty of 1/4 20 grade 5 with locknuts on things I’m not going to engineer.

Low stress, low consequence I use whatever is close at hand. If it’s going on a race car or motorcycle I definitely pay more attention.

There are plenty of applications where any fastener will do, just be sure those are the ones unknown hardware is used for.

John

 

[Deleted member 69715]

I may be out in left field here but for bolting stuff together where shear forces are present I use a grade 5 unless specified to use something else.
Clamping applications like connecting rod caps I'll reach for a grade 8.
Torque will vary by specific engineering requirement. In absence of that, I look at the material the fastener is threaded into. Softer material = less torque..
Works for me.

 

[Susquatch]

Most of what we do does not need higher grade stuff.

Even at the wholesaler the higher grade is much more expensive.

Most of our hardware is from lifetime of "finding", stainless from cell sites as tower crews drop lots, buckets of assortedfrom estate sales, one a farm with a wall of stuff to the sometime just buy them.

When we need the high grade we buy them, but for general stuff the cost sometimes just is not justified.

Yes, we are cheap, hard to justify a grade 8 1/4 20 bolt to hold a sheet metal (aluminum) into a threaded hole in relay rack.

Correct materials can save money better spent on other parts of the project.

We did buy only the grade 8 stuff for a short time as we were having some failures with some equipment.

But other stuff would fail instead which would be harder to fix, when the lower grade would fail it would give indication of failure, replace the bolt and tighten rest, inspect while there.

The higher grade would no longer be the weak link, now the thing that would cause the stress on the pert now instead of breaking a bolt now break the bracket the bolt is attached too.

Like putting a bolt into a fuse holder.

This is dependent on the specific circumstance, just something for consideration.

Sent from my SM-G781V using Tapatalk

Excellent common sense comments. They also happen to reflect what a good fastener engineer would say.

I think we all fall into the trap of stronger is better but it ain't necessarily so.

 

[Susquatch]

I may be out in left field here but for bolting stuff together where shear forces are present I use a grade 5 unless specified to use something else.
Clamping applications like connecting rod caps I'll reach for a grade 8.
Torque will vary by specific engineering requirement. In absence of that, I look at the material the fastener is threaded into. Softer material = less torque..
Works for me.

Yup, grade 5 is the grade of choice for shear applications - especially for shear bolt applications. Grade 8 will destroy a part and standard grade will bend before it breaks and be extremely difficult to repair.

Follow the manufacturers recommendations.