What grade/material fasteners should I be buying?

[tipo158]

I need to buy some suspension bolts for my Titan. Should I be getting Grade 5, Grade 8 or stainless?

alan

[John Robinson II]

AN or NAS is the only bolt to use properly sized and with washers on each end.

John

[Joe911]

Alan - althought there are many suppliers, the pegasus website is very user friendly with grip length listed for each bolt to help you determine the correct bolt for each of your applications.

[Jeff Owens]

NAS. Worth the $$$. www.coastfab.com Ask for Donnie. He is very helpful.

[tipo158]

OK, could someone tell me what why AN or NAS is required? (BTW, what is NAS? Plenty of places will sell them to me, but I don't see any of them explaining them!) My road cars are subjected to more extreme loads than my Titan ever will be and they don't use AN fasteners. Besides, wouldn't it be better if the bolt failed instead of the pick-up point?

alan

[Joe911]

National Aerospace Standard - Air Force Navy. An excellent discussion of this topic can be found in Carroll Smiths "Prepare to Win". If you don't own it - order one tomorrow. Wonderful treatment of race cars for laymen like us. "Tune to Win" is also great.

[TedV]

Also in Corroll Smith’s book Nut’s, Bolt’s, Fasterners and Plumbing Handbook is all about why. Depends on how the bolt is being used. But simply the threaded part will act as a file, enlarging the holes it is in, plus the threaded area when in shear is a stress riser and the bolt will fail very easy causing the suspension to leave the car, generally at the worst possible moment.

[tipo158]

Thanks for the info, guys.

I don't buy the material strength argument. (The Pegasus catalog quotes Carroll Smith from 1975 about how we should take the hint from the fact that the FAA does not allow SAE hardware for use in aircraft.) I also stage rally and I have used a lot of SAE hardware in rally cars and it holds up fine and those cars get the crap beat out of them. We do things like hit rocks at speed and drive at 95% of speed on flats until the tire (or even wheel) disintegrates. (OK, I am a co-driver, so I just watch the driver do that.)

However, the part about having the right grip length is good point.

I have an old Titan Mk6 front, upper control arm and damper bolt. You can see from the corrosion on the bolt that the grip length was about 9/16" shorter than it should have been for where the nut ended up when it was tightened. Also, what the grip should have been was very close to what it would have been for an AN bolt with the same nominal overall length.

alan

[Larry]

...and I've never hit my head while racing. Perhaps I should be allowed to race without a helmt--or at least just a $50 Wal-Mart helmet...


Just because it hasn't failed in the past, doesn't mean it won't fail in the future. You may never have a fastener fail, but if you do, it will likely cost you a lot more than the price of first-class fasteners. It may also cost one of your competitors if you are the root cause of an accident.

Larry Oliver
International Racing Products

[Brian]

there are two excellent reasons why people recommend and use AN fasteners rather than SAE fasteners - guarantee of quality, and correct grip length. Manufacturers of aircraft quality parts have to really focus on a good part every time. I've gotten SAE parts that were incorrectly threaded, for example.

SAE fasteners are designed for tensile applications primarily. SAE fasteners specifications do not have a specification for shear strength, only a conversion recommendation from tensile strength. SAE fasteners are usually a few thou. undersize on the grip diameters, so the AN parts will fit better in a reamed hole. Aircraft fasteners (AN, NAS, etc) are designed for shear applications and have a shear strength specification.

Common sense helps a bit here too. I have one car that uses 7/16" diameter bolts for all suspension applications. A quality 7/16" SAE grade 8 bolt in double shear is plenty strong for the suspension of a 1,000 pound car, and that's what I use. When you start getting below 5/16" for suspension bolts, then AN or better is a lot more critical. Using a great big super-bolt when the lugs are made of 16 Ga mild steel is false security as well.

NAS bolts are an upgrade from AN but you have to use a chamfered NAS washer under the bolt head. The washers are more expensive than normal AN washers but they are nice - hardened, chamfered, a little bigger than AN washers. Socket head cap screws are about the same strength as NAS bolts, are high quality if you get them from HK, Unbrako, SPS, etc, and can be a good choice also.

The thing about rally and production cars - and older formula cars, to be honest - is that they are designed to be put together with industrial quality parts. A 7/16" nail will be overkill for strength on a lot of cars. But more modern race cars are designed to closer tolerances and need the engineered strength of the correct fastener.

My take on this, anyway.

[racer27]

AN may be overkill, but I replaced all the critical fastners on my car with AN Grade... Larry Oliver has a hardware kit for the most common nuts, bolts, washers (They are a system ansd should be used together). A kit will last you several years and is a permanant fixture in the trailer. Also avail from AirCraft Spruce (The racers hardware store) or Wicks or Coast Fab.

[Jtovo]

I will second Aircract spruce. I just bought some and it was sent out the same day. I also picked up the AN chart, so you order the correct stuff.

I think my numbers are correct, if not, I am sure that John will correct me (and I welcome that).

Pegasus was like $2.34 per bolt and Aircraft Spruce was about .70 per bolt.

[Dave Hopple]

http://www.wicksaircraft.com/ I've been buying all my hardware from Wicks Aircraft supply, prices and selection are very good, they have a online ordering option also. -Dave

[tipo158]

...and I've never hit my head while racing. Perhaps I should be allowed to race without a helmt--or at least just a $50 Wal-Mart helmet...

Just because it hasn't failed in the past, doesn't mean it won't fail in the future. You may never have a fastener fail, but if you do, it will likely cost you a lot more than the price of first-class fasteners. It may also cost one of your competitors if you are the root cause of an accident.

You don't know me and you don't my race history or shop practices, so I don't know how you can make statements that imply that I haven't seriously looked at this issue. I am trying to discuss the merits of one fastener spec vs. another, not get into a "won't you feel bad if you don't buy the most expensive part available and someone gets hurt" discussion.

As far as that $50 Walmart helmet, is it SA-2005 certified?

alan

[flat broke]

Easy Alan. People have taken the time to offer a response to a valid question. The problem with these postings is that they can sound critical even when trying to be helpful. May I suggest that you take the advice and evaluate it without being too defensive. I assure you that the answer to your question lies within the responses and the books that were referred to.

Tony

[EYERACE]

for some simple applications - grade 8 or even less [what grade are the bolts in a hose clamp?] - but when stress is a known factor....why not spend the little extra that it takes to have confidence.

the parable about how the king lost his kingdom because his army lost the battle > > > for want of a nail the shoe was lost, for want of a shoe the horse was lost, for want.......i'm sure ya'll have heard this one before. but if you merely want the horse to plow the field....you can use your wife!

[Charles Warner]

Alan,


If you race your Titan hard it will experience more stress than a street car. The AN bolt are consistent and reasonable and can be specifically tailored for each application.

[Daryl DeArman]

I think Brian covered it well.

I also service and have been ballast on a Grp2/5 rally car. I can tell you, with absolute certainty, that the stresses encountered on a Rally suspension and chassis FAR exceed anything a FF will see.

However, the Production based rally cars have many components that are designed with such a huge safety factor built in, that some parts are adequate strength for a Rally because of their SIZE not material strength.

Older FF's (Crossle 32) for example have huge rod ends...way stronger than they need to be. A later car does not.

[Greg Mercurio]

tipo: Re-read Brians post.


Also, do yourself a little experiment. Get some brand new Grade 5 bolts, some brand new Grade 8 bolts, and some brand new AN bolts. In this case, size DON'T matter.

Measure the diameter of the bolts at 3 or 4 places checking for roundness. Repeat along the grip length. Compare data.

If you've got access to a precision lathe, check perpendicularity of the shank to the compression face of the hex. Compare data.

Take a real hard lood at the runout of the thread where the grip portion starts. Compare data.

Take 3 of each and put them outside for a month exposed to the weather. Compare data`

See if you can find someone with access to an Instron Tensile Tester or similar. Test to failure a sample of each. Compare data.

After all this, use whatever you think is required to meet your standards.

Everyone of us has already made that decision.

[tipo158]

Easy Alan. People have taken the time to offer a response to a valid question. The problem with these postings is that they can sound critical even when trying to be helpful. May I suggest that you take the advice and evaluate it without being too defensive. I assure you that the answer to your question lies within the responses and the books that were referred to.

I was only critical of Larry's response; I thanked everyone else. I don't think I was being defensive; I was specifically responding to Larry's implication that I want to cut costs at the expense of safety (when, in fact, I had already implied that I would be getting AN hardware).

However, I don't think the matter has been completely discussed. What about the idea that it is better to have the fastener serve as the sacrificial element in the suspension than, say, the suspension pick-up? Should anything be inferred from the fact that my Titan came from the factory with SAE hardware? What about the idea that metallurgy has changes since most of the standard books were written and have fasteners gotten better or worse as a result of the tug-of-war between advances in technology vs. the desire to drive cost out of everything?

The thing that I learned from upgrading components on my 70s vintage Lotus road cars is that you usually end up just moving the problem that you were trying to solve by upgrading.

In the end, I was trying to promote an actual discussion on this forum, which doesn't seem to happen much.

alan

[Jtovo]

My biggest reason for AN hardware, is the thread/body length. Most of the hardware going on suspension, needs short threads. I do not want a threaded piece running through my shock, too much tolenance.


If you are bolting your engine to the frame, use grade 5 or whatever, not such a big deal.

[DanW]

[size=2]I am a bit surprised no one has mentioned material specs.[/size]

[size=2]The Grade 5 and Grade 8 fasteners you find at the hardware or auto parts store may be just fine. Or maybe not. Fasteners are made by cold heading thick wire in a press, parted off to length by shearing, and the threads are formed by rolling the shank between the thread forming plate. Its a simple and repeatable process. Most common fasteners are now made outside the US because the cost of labor and energy are so much less, just like everything else. [/size]

[size=2]Fasteners are commodity items to all but the aviation industry. There are more choices for grip and overall lengths and the dimensional tolerances are closer. Few aviation fasteners and other materials are made outside of Europe and the US. [/size]

[size=2]When Mr. Boeing or Mr. Lockheed buy fasteners by specification, they insist on material test reports or at least a certificate of conformance to the AN or NAS specifications. The QA department will pull a shipment off the dock and lock it up in the non-conformance cage if the paperwork is missing. The materials department may take a representative sample and perform dimensional inspection and tensile test to make sure it meets the specification. If it doesn't, the shipment is returned to the vendor. [/size]

[size=2]Most of the stuff we see here on the west coast is marked 'KS' on the head. KS stands for Korean Steel. The bulk boxes I have seen at the local Grainger and Motion Industries stores in South San Francisco are from China and India.[/size]

[size=2]This doesn't give me confidence about those fasteners meeting quality or metallurgical specifications. There is no one between you and the manufacturer in Nanking who makes sure the chemical, physical, and mechanical properties meet the standard for Grade 5 or Grade 8 (available in the Machinery's Handbook). No matter how the bolts are marked, they may be the ISO 8.8 grade (lower tensile and yield than Grade 5) or even Grade 2 (low carbon steel).[/size]
[size=2][/size]
[size=2]My point is, know what you are buying. Caveat Emptor[/size]


[size=2]Just my $0.02[/size]

[Charles Warner]

What year is your Titan? AN/NAS bolts have not always been available, especially in Europe.

[Jonathan Hirst]

I always thought the Titan was very forward thinking in the sizing of it suspension bolts. Parked beside one another, the Titan suspension made my Crossle 16F look like a tractor.

For the Titan more so than many vintage FFords, I would go with AN.

For the time invested in properly sizing grip lengths (and cutting down the threads for) the SAE bolts, the time saved alone by using AN hardware is worth it to me.

Jonathan

[Larry]

I need to buy some suspension bolts for my Titan. Should I be getting Grade 5, Grade 8 or stainless?

alan

...so you asked a question, and you received many responses from many people with a lot of experience. Most stated their reasons for selecting either AN or NAS--then you proceed to disagree with the responses. Why did you bother to ask, if all you wanted to do was argue?

Larry Oliver
International Racing Products

[Brian]

I look at it this way. The 5/16" bolt that fastens the rear radius arm rod end of the suspension of my Lola has a diameter of .3125" and a cross-section area of .0766 square inches. An AN bolt has shear strength of 90,000 PSI (from memory, may be a little less, Coast Fab catalog is at home). So that bolt has a single shear strength of 6,900 pounds more or less, and since it's in double shear, that's 13,800 pounds. The lug it's attached to is 16 ga mild steel doubled locally to 1/8". The radius of the shear area of the lug is .2", so the shear area is .025". I don't know the shear strength of mild steel with a washer brazed to it as a doubler, but let's give it the same 90,000 PSI (it's probably way less). The single shear strength of the lug is 2,250 pounds, the double shear strength is then 4,500 pounds, there's two lugs so 9,000 pounds total or less than two thirds of the strength of the bolt.

Grade 5 SAE, while having all of the issues that we've discussed, is nominally similar in strength to a AN bolt. Grade 8 is roughly 20% stronger. If there are no engineering reasons for using AN other than strength, I'll put it to you that since the lug is by far and away the weakest link in this equation, it matters not a fig what kind of bolt you put in there. One that has nice pretty plating is good, and I wouldn't personally use stainless or Grade 2.

I get a little frustrated when people say "use AN because it's stronger". The plain fact is that it's usually isn't stronger in any meaningful way, and it almost never is the designed weak link in the system. All AN is, as far as I am concerned, is the right length. And guaranteed quality. And good for people who have little engineering knowledge (read part time crew who is impressed by not using a pipe wrench to nut and bolt the car) so that they can't make a mistake about putting a good enough bolt into an application. And a PITA to get, to stock in meaningful quantities so that you can actually do a job today instead of next week, and expensive if you add in shipping to the entirely reasonable cost of the actual fastener.

I grant that many cars need and must have aircraft quality fasteners. Probably Formula Fords made prior to about 1980 aren't in that group. I grant that aircraft quality fasteners are better in quality than most SAE stuff, and that's it's good practice to put them on your car particularly if you don't know if they are needed or not. But for AN in particular they aren't stronger and strength isn't why you use them. NAS, etc are stronger. There are lots of bolts stronger than that. But not AN.

Cheers, Brian and sorry for the rant.

[Charles Warner]

Brian,

Rant away, but direct it at your importation regulators. Most of us can order AN stuff on-line and get it next day. Greatest differences, as have been pointed out, are consistency, quality and ability of getting the exact thread length you need.

[Greg Mercurio]

Great post Brian, but there is another reason to use the AN bolt. The tolerance on the diameter of the 5/16 bolt is going to be far closer to the theoretical .3125 on the AN bolt than on the Gr5 or Gr8. Easy enought to test if you have a micrometer. The plating tolerance is also critical to maintaining this diameter. AN bolts are controlled from raw ore stocks to supplier, and as Dan W pointed out are certified.

Adding cyclic fatigue to the above stresses changes the picture a bit. Since FF's all have resonances somewhere in their RPM bands, it's Russian Roulette. Only there are other people in the game on a track. They probably won't like to be included in the game.

[Charles Warner]

One other point regarding the use of AN bolts. Often your standard Home Depot drill bit will not be sized as acurately as the AN bolt. I find a set of reamers to be invaluable. Certainly better than going the next size up on a drill bit.

[Brian]

All I'm really saying is that AN fasteners are many things, but they aren't really very strong. I worry that people sieze on AN as some sort of gold standard, when all they really are is a good quality medium strength faster, at 125Kpsi. If you are looking at suspension pieces and worried about load factors, then I wouldn't recommend AN without doing some analysis. In my example above, AN would be fine, but in other cases maybe a MS 21250 bolt would be the right choice. In other cases, a Grade 8 bolt will be fine, and it's true that a lot of cars were designed to be assembled with SAE and SHCS fasteners, no aerospace in sight.

I totally agree that in a lot of applications, AN, MS, NAS are the correct choice for a lot of reasons. But there are all sorts of applications that don't call for them - where they aren't the best choice all things considered. But they will never be a bad choice either.

I got into and learned about this years ago when I was looking for a rod bolt for a set of Martin FJ rods that I had. ARP didn't make one, and I was convinced that I needed a super-bolt because I always used ARP. I eventually found a 3/8" NF thread bolt, 12 point head, 1.25" long, 325KPSI, that cost about $300 each in quantity of 8 - it was for something inside of a Rolls Royce jet engine. I didn't buy them, even though they were the strongest bolts I had ever heard of! I used MS21250's instead, at 180KPSI.

Brian

[Paul LeCain]

[size=2]No one has mentioned this here, so I will. The biggest difference I see is not ultimate strength of the bolt. No one is ever going to approach that stress level short of a major shunt.[/size]
[size=2][/size]
[size=2]In all the accidents I've seen on our cars, the AN/NAS bolts have bent pretty severely, but I've never seen one break. [/size]

[Rick Kirchner]

If I recall, strength isn't the only factor, toughness comes in to play. I recall one of the issues with grade 8 stuff is that along with the strength you get brittleness, and that's not the case with the AN stuff.

[Rick Kirchner]

.....

[formulasuper]

One other point regarding the use of AN bolts. Often your standard Home Depot drill bit will not be sized as acurately as the AN bolt. I find a set of reamers to be invaluable. Certainly better than going the next size up on a drill bit.

Also, reamers make a much smoother hole which helps prevent fatique failure of the part being drilled. All aircraft structure holes are drilled in steps with the final reamer leaving a polished looking hole inside. They even check every hole with test probes & record the findings by blue print hole numbers in the manufacturing records.