Grade 5 vs Grade 8

I was recently told that Grade 5 hardware has better shear strength than Grade 8 hardware. I was very surprised to hear this so I did a quick google on it. I came up with this excellent report on this exact subject matter.

http://www.rockcrawler.com/techreports/fasteners/index.asp

Also, the index for the tech articles looked very promising

http://www.rockcrawler.com/techreports/

Hopefully this will help some folks.

Links didn't work for me but whoever told you that 5 has a higher shear strength then 8 was lieing or guessing wrong. It doesn't!

Grade 8 has both a higher shear and tensile than 5.

The only strength measurement that I believe 5 exceeds 8 in is "toughness". I'm going back a few years on the Mat Sci here but IIRC "toughness" is a measurment of a material's ability to absorb energy in failure.
It would take a higher force to break a Gr8 than a Gr5 but the 5 would absorb more energy when it actually fails.

yep.

I am so sick of the myth that "grade 5 is stronger than grade 8, cause grade 8 snaps".......

physical data is physical data. it is not subjective.

grade 8 is stronger than grade 5.....

period.

Just as a side note...... the link and text are reversed. I.e. what should be the link is what is displayed. Copy the text and paste it in your browser address bar to bring up the page.

Thanks for the data.

Just to humor this thread a little more.....

There could be real world circumstances where a Gr 5 could conceivably outperform an 8.
Since the Grade 5 has a much lower yield strength than Gr8, it will deflect at a lower force and through a greater distance before failing. If a condition was such that an applying force were to decrease substantially with only a small amount of deflection, it 'could' be possible for a Grade 5 to deflect through that distance, thus reducing the force to below the yield strength of the bolt. In the same application a Gr 8 may not deflect enough to reduce the force to below the strength of the bolt.

An imaginary example of this might be where a length of metal is fixed rigidly at both ends and heated. Thermal expansion of the metal will apply a compressive force to the fixed ends but it cannot apply that force through a very long range and it decreases exponentially with travel distance. A small amount of deflection on the fixed ends will result in a dramatic reduction in the compressive force.

A completely and totally hypothetical scenario only. Please don't try to apply or rationalize this into a reason that 5 is stronger. It isn't.

Just leave it as Beezil says;
"8 is stronger. End of story"

Now, stop imagining.

Muscle braining a bolt, instead of using a torque wrench. Will stretch grade 5 bolts fairly easily. Grade 8 bolts, in normal automotive sizes are less suseptable to stretching, with normal half inch drive ratchets.
What I´m saying is, a torque wrench, in may applications, is more important with the grade five.
My general rule of thumb is grade five for constructions and fasteners. Grade 8 for loaded (stressed) or machine (mechanical) applications.
Don´t know if it´s fact or fiction, but platings or anti corrosives on bolts (eventual electrolysis?),are said to affect the ratings. Just for safties sake, I´ll usually bump one grade for treated hardware.

its all in the numbers.

you can't rework them.

Sorry about flubbing the links. Here's another link that I found informative:

http://www.nkn.com/pdf/fastener.pdf

And here's something else to consider. If I am using button head fasteners to hold up plating under the rig, which would be better to have, Grade 5 made of medium carbon steel, or Grade 8 made of medium carbon alloy steel?

In this application I am assuming there are no significant tension or shear forces being applied to the bolts. Most of the abuse should be transferred through the plate (in a vertical direction) to the frame rails. Therefore Grade 8 does not seem necessary.

So the question is, when rocks start smashing the fastener heads, which will put up with it better?

It is an interesting characteristic of pretty much anything that if you increase its strength, you increase its brittleness as well. Therefore, while 8grade fasteners are significantly stronger than 5grade in both tensile and shear strength, the 5grade will have a higher tolerance for "plastic" deformation (stretch and suchlike) than 8grade of equal size.

What to use where? Depends on application. I'd probably use something like brass for anything exposed to the elements that does not require significant tensile or shear strength (non-structural panel work, simple retention undercar, &c) vice alloy steel or CRES simply because I'd be more interested in corrosion resistance than in brute strength. As a result, I use a LOT of brass! (No, I've not had a fastener failure as a result.)

If I'm worried about fastener strength in a tensile plane (along then length,) fastener design becomes just as important as material. Without wandering into exotic profiles, some of the strongest fastener shapes you can get for machine screws are the socket head screws in Torx or hex socket. By lessening the relative size difference between the head and the shank of the fastener, stress risers are reduced and overall strength is increased as a result. A socket head will have greater tensile strength than a hex head fastener in the same nominal size and material. This has to do with the flow of "stress lines" through the fastener body. Note that tensile strength is measured in ksi (thousand psi,) so increasing the nominal diameter will also increase available tensile strength. However, this does not necessarily make up for shonky design or bad fastener choices.

If I am looking for shear strength, I will go for a larger nominal diameter to offer more area to the stress plane. Why? More material can equal more strength.

Note that ANSI grade levels trypically are only applied to carbon alloy steel - CRES alloys and nonferrous alloys answer to their own specifications. Getting you hands on a recent copy of Machinery's Handbook is always a good thing - but another excellent book on the subject is "Nuts, Bolts, and Plumbing" (or something similar!) by Carroll Smith - and I usually spot it at Barnes & Noble in the "transportation" section for a tad less than $20. It's written in layman's terms and well-presented by an individual with a great deal of experience and a pleasing dry wit - much easier to read than MH!

5-90

Where do you guys normally get Grade 8 bolts at? I just replaced the bolts that hold my crossmember on because I needed longer ones to run through the T&J skids, and I used Grade 5 because that's what I could find at Lowes and I didn't think those bolts would bear much load. I'd almost always be willing to pay the extra $$ for Grade 8, but where is a convenient place to get them?

Any shop with a decent fastener selection should have both grade 5 and 8 bolts. Ace Hardware, Home Depot, etc. Or the big fastener outlets like Fastenal.

xj92 said:

Where do you guys normally get Grade 8 bolts at? I just replaced the bolts that hold my crossmember on because I needed longer ones to run through the T&J skids, and I used Grade 5 because that's what I could find at Lowes and I didn't think those bolts would bear much load. I'd almost always be willing to pay the extra $$ for Grade 8, but where is a convenient place to get them?

Click to expand...

"Ace is the place"
Or Copperstate Nut and Bolt here in AZ.

Check around - I get my hardware down the street at Orchard Supply Hardware (5grade, 8grade, CRES Alloy, and Half Hard brass) without any trouble. Most of their CRES is 304SS or 316SS, both of which are good G/P CRES alloys.

You shouldn't need anything more exotic than that usually - but Fastenal carries silicon bronze (good for high heat/low strength, like exhaust) and 9grade ANSI, as well as metrics out to 12.9 IIRC. They're online, your locator will probably turn up something close, and their prices aren't too bad...

Only catch is that it doesn't pay to be too picky these days - I prefer US, German, or Japan-made hardware, but most of what is available is Taiwan, Chinese, or other "minor" maker. Pity...

5-90

Get your grade 8 from TSC (tractor supply company)

Sometimes I get lucky and find a Pep Boys that carries hardware. They will have a large selection of 8, 8.8, 9.8, and 10.9 graded hardware. The only good I've found for this store.

The one in Henrietta, NY is one such store.

--Matt

D&B Supply sells grade 8 by the pound. About 1/10th the cost of Home Depot or Lowes. Fastenal is cool too if ou are buying in bulk.

Farm-n-Fleet sells bolts by the pound, mix and match. All Grade 5 is one price, Grade 8 another. Unfortunately, not metric, but it was still a cheap and easy way to get a fairly complete assortment of SAE bolts, nuts, and washers. FWIW

xj92 said:

Where do you guys normally get Grade 8 bolts at? I just replaced the bolts that hold my crossmember on because I needed longer ones to run through the T&J skids, and I used Grade 5 because that's what I could find at Lowes and I didn't think those bolts would bear much load. I'd almost always be willing to pay the extra $$ for Grade 8, but where is a convenient place to get them?

Click to expand...

Nearly every community has a nut and bolt store that specializes in fasteners of every type. If you haven't been in one, they are very cool.....even beats the hell out of Harbor Freight.

Check the yellow pages. Bakersfield isn't a real large city and I still have three of them within five miles of my house.

Just went over this in my engineering class....material science....I'm backing Beez' all the way, numbers dont' lie especially when they are subjected to test after test after test to determine shear strength's and tensile strengths