SAE Grade-8 bolt snapped @135ft/lbs

[avbug]

I'm dealing with a critical application. If these fasteners fail, the results could potentially be fatal. I need maximum security.

Gee, guess I made the mistake of listeing to you the first time around. Critical, could kill you, need maximum security. Sounds like a job for home depot to me.

Always look to the lowest bidder.

Incidentally, there is NO comparison between "grade 8" and AN or NAS hardware. Further, there is no uniform quality control or anything like standard order for grade 8 bolts. Yeah, they're supposed to conform or be capable of a particular standard, but don't bet on it. You get what you pay for (and sometimes not even that). Overtorque few and see how uniform they are in their capabilities, and how many will pop a head off before they shear...you may be surprised how low the standards really are, and how inconsistent.

But hey, it's only a "critical application" that could "be fatal," that requires "maximum security." It's only your truck. Do whatever you like. You're going to, anyway.

 

[UnAnswerd]

But hey, it's only a "critical application" that could "be fatal," that requires "maximum security." It's only your truck. Do whatever you like. You're going to, anyway.

All vehicle manufactures use SAE (or ASME) hardware, even in vital suspension components. I think it stands to reason that a true grade-8 bolt will be more than adequate in dealing with the loads imposed by my particular application. Your suggestion to use aircraft-type hardware is appreciated, but it remains my honest opinion that regular SAE hardware will be acceptable.

 

[avbug]

Yet it failed you, and you wanna know why, for your "critical" application which "could be fatal." And let's not forget, you didn't seek out an automotive forum, you asked the question in an aviation maintenance forum.

Now that I think about it, were you not the one who was arguementative to the point that several responsible posters on this site finally refused to communicate with you any further?

In fact, now that I think about it...I think one of them was me...

 

[UnAnswerd]

Now that I think about it, were you not the one who was arguementative to the point that several responsible posters on this site finally refused to communicate with you any further?

Go back and read the "accident" thread. I asked a simple question and was given Hell for it. As far as this thread, note that I only asked for a torque value, not which class of fastener to use. Again, your suggestion is appreciated, but it remains my belief that SAE hardware will suffice. The bolt in question may have failed for several reasons. General commercial fasteners have indeed been mismarked with SAE markings. So have aircraft bolts for that matter. I'm not arguing, just upholding my opinion. There is a difference....

 

[Flyin Tony]

it is too expensive, not readily available

You can get almost any AN bolt from aircraft-spruce http://www.aircraft-spruce.com/

http://www.aircraftspruce.com/menus/ha/bolts.html

 

[troy]

I'm a little late, but my torque specs say 91 ft/lbs for unplated/silver plate, and 117 for plated (gold)

 

[Dave Danger]

SAE Grade-8 bolt snapped

After reading all the above, it is obvious that for whatever reason, the originator has a reason that he'd rather use grade 8 (hardware store) bolts than something that may have more than enough tensile strength. "Shrug the shoulders" and go sideways around the tree. Use more of them (bolts) for the application that he's after. Assuming the application will allow it, use 2 or even 3 bolts instead of 1 to do whatever the job is. Less torque will be required as the load will be shared.
Think outside the box a bit.

Dave Danger

 

[avbug]

Dave,

I don't think it's so much about thinking outside any particular geometric pattern (love that expression about boxes, it should be the banner motto for yuppies everywhere) as a poster with an attitude and a short fuze.

 

[UnAnswerd]

the originator has a reason that he'd rather use grade 8 (hardware store) bolts than something that may have more than enough tensile strength.

You cannot compare SAE fasteners to just any "hardware store" bolt. The truth is, each SAE grade is manufactured to meet certain tolerances. That's why these fasteners are widely used in the automotive industry to hold critical parts together. If they weren't made to specific tolerances, the auto manufactures wouldn't risk billions of dollars in lawsuits by using them.

The reason many people claim that SAE grades do not meet specific tolerances, is because sometime in the 1980's a very large volume of hardware was imported into the united states with false SAE markings. It remains a problem to this day. Regardless, if the appropriate paperwork can be furnished with purchase of SAE fasteners, they WILL meet specific tolerances. In the case of grade-8 hardware, it is a 150,000psi tensile-strength.

 

[avbug]

SAE provides "standards," but there is no quality control nor consistency in the parts. The FAA has put out numerous warnings about the use of Grade 8 hardware...weather or not one chooses to use this hardware on aircraft is beside the point; the warning is valid. The parts do not show consistency, which is why they're not approved for use on aircraft. If tensile strength were the only issue, they'd be fine, but there is no quality assurance in grade 8 hardware.

Again, do what you will for the critical operation upon which your life depends. Don't however try to hold out automotive standards as some high level of quality, because they're not. Automotive parts are made based on economy, and it's far easier to replace a defective cheap part in the automotive industry than manufactur higher quality equipment. Automotive standards are rough, often not overly exact. Rather than build a quality part for a car, usually the part is just built bigger.

Most of your hardware store bolts (or automotive store bolts, if you prefer) have tensile strengths closer to 60,000 PSI or less, with Grade 8 at a shear value of 91,000 psi and 150,000 ultimate (in theory), while AN bolts are 125,000 psi. Hardware store SAE bolts are mostly not corrosion resistant, and bend easily. AN bolts are nickle alloys, while SAE Grade 8 bolts are mild steel. AN bolts are more ductile, while SAE Grade 8 are more brittle. AN hardware and SAE hardware have very different thread load bearing properties and capabilities. AN, NAS, and MS bolts (aircraft grade hardware) are consistent in properties, qualities, and standard from lot to lot. SAE Grade 8 hardware is NOT. AN bolt threads are rolled after heat treating, whereas SAE are cut afterward.

All AN hardware has the same properties. Grade 8 hardware has vastly different properties that vary with manufacturer and lot number. Where the AN hardware is rolled, often the SAE Grade A threads are cut, and that's one of two places the bolts tend to break. Yours twisted off with torque, I believe. Did it twist off in the threads? The other place these tend to break is the head, owing both the britleness,and the inconsistency in radiusing the head and shank.

You'll note I listed alleged tensile strengths. Tensile strengths for SAE Grade 8 can only be approximated, due to the variance between lots. This is not the case for NAS, MS, or AN hardware, and that's a very important distinction.

You mumbled something about not confusing SAE hardware with hardware-store hardware. I don't want to burst your bubble (actually, I do), but hardware store hardware IS SAE. It may nor may not be Grade 8, as numerous grades exist, but all the standard bolts and sizes you find are SAE bolts...just with varying degrees and qualities of production. Grade 5 is SAE. So is Grade 8. Grade 5 has lower tensile strengths, but tends to bend more, is less brittle, and may actually do better than the Grade 8 in many cases. Of course, you need to specify weather you're after actual tensile strength (as in holding the threads or headof the bolt on) or shear strength. In either case, test out several examples purchased from different sources in the SAE, and you'll find numerous different failure points...showing clearly the lack of consistency in production.

You cannot compare SAE fasteners to just any "hardware store" bolt. The truth is, each SAE grade is manufactured to meet certain tolerances. That's why these fasteners are widely used in the automotive industry to hold critical parts together. If they weren't made to specific tolerances, the auto manufactures wouldn't risk billions of dollars in lawsuits by using them.

Actually yes, the hardware store bolts are SAE bolts. Not all grade 8, but still SAE...unless they're metric.

If they weren't made to specific tolerances, auto manufacturers wouldn't take the risk? No? Why do you suppose the FAA doesn't permit or authorize their use? Think about that a little before you reply.