# How do I test unknown bolts?



## Batmanacw (Jul 24, 2022)

On Saturday I bought around 150 lbs of bolts in ten coffee cans at the flea market. A steel basket full of 1", and 7/8" bolts was probably 75# by itself. 

They were kind of sorted but not really....... 

I ended up with lots of 5/16, 3/8 and 1/2" in almost every size.  

Many of them are unmarked grade 2 in raw steel. Uncoated. They look to be very good quality. 

I would like to test a couple just to see if the hold up the way they should. What torque should break a grade two 3/8 or 1/2" bolt if properly lubricated?

I also ended up with lots of oversized nuts in 5/16, 3/8, and 1/2. I've only seen a few of these and now I've got hundreds....lol!


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## David2011 (Jul 24, 2022)

A quick search found this.  It’s torque specs rather than breaking specs but if the fasteners exceed the specs you should be good.  Specs for wet and dry torque are listed.   https://mechanicology.com/sae-bolt-torque-chart-grade-2-grade-5-grade-8


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## benmychree (Jul 24, 2022)

Oversize nuts are called "heavy hex nuts"  Good for shop use, they don't round over easily.


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## Jake M (Jul 24, 2022)

Batmanacw said:


> On Saturday I bought around 150 lbs of bolts in ten coffee cans at the flea market. A steel basket full of 1", and 7/8" bolts was probably 75# by itself.
> 
> They were kind of sorted but not really.......
> 
> ...




Torque to breaking wouldn't be a valid test on a bolt that you don't have an entire chain of custody of, chemestry and surface of the coating, full control over, and heaven forbid any patina or weathering.  

If you've got grade 2 or ungraded bolts, they're cheeze grade mild steel, not structural, treat them like you just cut them yourself out of a hot rolled bar.  Technically grade 2 (unmarked) is on the high side of that, it's not a big margin at all.  Not tangible in a DIY testing method.  Yes, you "could" do more things with grade 2 than with ungraded, HOWEVER, that is the very same marking system used for bolts that did not ever claim a grade 2 rating.  The difference between the two is small enough that you're not going to figure it out without lab grade equipment.  In practice, without a controlled surface finish, without a controlled friction invironment for the rotating face of the bolt head or nut, and using torque as your metric, there's about a one hundred and six percent chance that you're probably gonna convince yourself that the unmarked bolts exdeed grade 8.  Unless they're truly not graded (same lack of markings as grade 2), and maybe they're made out of aluminum or zinc or plastic or something....  If they're steel, they are (for all intents and purposes) cheeze grade hot rolled.

Unmarked AND uncoated is a bad omen towards these being anything notable.  Any bolt that has any importance or consequence or significance, is finished with something.   Plain finish bolts don't see a job where they're counted on to provide any significant strength or clamp load.

What do you intend to do with them?  Fastening jobs, or turning stock?


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## Ulma Doctor (Jul 24, 2022)

soft bolts can be used anywhere high strength is not a prerequisite
even soft bolts can give thousands of pounds of clamping force, especially in large diameters
the softer the fastener, the more it is likely to deform, rather than break (within limits of course)


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## Batmanacw (Jul 24, 2022)

Jake M said:


> Torque to breaking wouldn't be a valid test on a bolt that you don't have an entire chain of custody of, chemestry and surface of the coating, full control over, and heaven forbid any patina or weathering.
> 
> If you've got grade 2 or ungraded bolts, they're cheeze grade mild steel, not structural, treat them like you just cut them yourself out of a hot rolled bar.  Technically grade 2 (unmarked) is on the high side of that, it's not a big margin at all.  Not tangible in a DIY testing method.  Yes, you "could" do more things with grade 2 than with ungraded, HOWEVER, that is the very same marking system used for bolts that did not ever claim a grade 2 rating.  The difference between the two is small enough that you're not going to figure it out without lab grade equipment.  In practice, without a controlled surface finish, without a controlled friction invironment for the rotating face of the bolt head or nut, and using torque as your metric, there's about a one hundred and six percent chance that you're probably gonna convince yourself that the unmarked bolts exdeed grade 8.  Unless they're truly not graded (same lack of markings as grade 2), and maybe they're made out of aluminum or zinc or plastic or something....  If they're steel, they are (for all intents and purposes) cheeze grade hot rolled.
> 
> ...


They will be handy for all kinds of low stress jobs I get in my shop. I have repaired farm carts and feed processing equipment that don't require extremely strong bolts. Holding a small motor on a feed conveyor isn't hard.

I'll save my grade 5 and 8 for higher stress stuff. Its not hard to gauge situations where higher grade is necessary.

ETA: these bolts could be pretty old. I think the guy who sold them bought out a farm shop decades ago.


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## matthewsx (Jul 25, 2022)

Here's a simple test from the marine industry for unknown or damaged hardware. 

Take it to the nearest marina, toss it into the water. If it floats it's good, go ahead and install it in your critical application.

John


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## Batmanacw (Jul 25, 2022)

matthewsx said:


> Here's a simple test from the marine industry for unknown or damaged hardware.
> 
> Take it to the nearest marina, toss it into the water. If it floats it's good, go ahead and install it in your critical application.
> 
> John



I'm not in the marine industry. These are not completely unknown or damaged.


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## Batmanacw (Jul 25, 2022)

My first attempt at testing gave a significant result. I took six lubricated 3/8-16 grade 2 bolts to failure. They all failed at 35 to 40 ft lbs. 

I took one grade 5 bolt to failure at 55 ft lbs. I'm not wasting a bunch of those.....

No grade 8 bolts were harmed during testing. Lol!

There is plenty of places these bolts will be useful. Of course not in high stress applications.


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## RJSakowski (Jul 25, 2022)




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## ericc (Jul 25, 2022)

Spark test.  You will have no problem distinguishing medium carbon from mild steel.  Difference between grades 5 and 8 will be harder.  Maybe a file or test?  The late, great guru of anvilfire.com cautions against depending too much on the extra strength provided by grade 8 over grade 5.  I bought a box of mystery drill bits.  Some were simple carbon steel.  They were impossible to keep sharp.  Ended up retiring all of them (that doesn't mean throwing them away).


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## Batmanacw (Jul 25, 2022)

ericc said:


> Spark test.  You will have no problem distinguishing medium carbon from mild steel.  Difference between grades 5 and 8 will be harder.  Maybe a file or test?  The late, great guru of anvilfire.com cautions against depending too much on the extra strength provided by grade 8 over grade 5.  I bought a box of mystery drill bits.  Some were simple carbon steel.  They were impossible to keep sharp.  Ended up retiring all of them (that doesn't mean throwing them away).


I already know which bolts are grade 2, 5, and 8. I wanted to know if they are up to nominal specs. 

The grade 2 made it to almost double the rated torque specs. 35 to 40 ft lbs. I'm not dissatisfied. They are rated for 20 ft lbs lubricated.


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## Batmanacw (Jul 25, 2022)

Forgot to post pictures. They all failed in the same spot.


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## RJSakowski (Jul 25, 2022)

Bolt torque failure isn't a good indication of bolt strength.  Torque specs for fasteners are intended to provide guidance as to the maximum amount of torque that can safely be used without damaging the fastener threads.


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## BGHansen (Jul 25, 2022)

This is from a Google search - bolt head grade markings

Bruce


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## Batmanacw (Jul 25, 2022)

RJSakowski said:


> Bolt torque failure isn't a good indication of bolt strength.  Torque specs for fasteners are intended to provide guidance as to the maximum amount of torque that can safely be used without damaging the fastener threads.


It did show a clear difference between grades.


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## ClintNZ (Jul 25, 2022)

RJSakowski said:


> Bolt torque failure isn't a good indication of bolt strength.  Torque specs for fasteners are intended to provide guidance as to the maximum amount of torque that can safely be used without damaging the fastener threads.


Torque to failure may not be a 'good' indication of bolt tensile strength but surely both values would always increase together? Would be really interested to know where that relationship does not apply to the world of common fasteners.

Cheers
Clint


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## aliva (Jul 25, 2022)

If you find any marked A325 Those are structural torque spec is above 300lbs. keep them for the real serious jobs. From a farmer your not likely to come across any of them.


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## matthewsx (Jul 25, 2022)

Batmanacw said:


> I'm not in the marine industry. These are not completely unknown or damaged.


I hope you didn't take offense. Use them as you will but keep in mind the next person who comes across them may not be as diligent as you are.

This is my favorite reference book on the subject:





__





						www.CarrollSmith.com -- NUTS, BOLTS, FASTENERS, and PLUMBING HANDBOOK
					





					www.carrollsmith.com
				




Cheers,

John


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## Susquatch (Jul 25, 2022)

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.


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## Batmanacw (Jul 25, 2022)

Susquatch said:


> 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.
> 
> ...


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.


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## sdelivery (Jul 26, 2022)

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.


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## Batmanacw (Jul 26, 2022)

sdelivery said:


> 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.


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## Susquatch (Jul 26, 2022)

sdelivery said:


> 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.


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## sdelivery (Jul 26, 2022)

Susquatch said:


> 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.


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## tq60 (Jul 26, 2022)

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


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## matthewsx (Jul 26, 2022)

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


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## Bone Head (Jul 27, 2022)

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.


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## Susquatch (Jul 28, 2022)

tq60 said:


> Most of what we do does not need higher grade stuff.
> 
> Even at the wholesaler the higher grade is much more expensive.
> 
> ...



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.


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## Susquatch (Jul 28, 2022)

Bone Head said:


> 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.


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