All you want to know about bolts...Grade 5 or 8 or aircraft or whatever....

[jerryweichers]

specialk,
i have not ever nor would i compare my ability to carroll smith. in fact i believe he is on the record that hardware store bolts have no place in a race car . i also believe he taught that if you have to use other than air craft hardware you should buy them at a farm / heavy equipment /tractor supply and only use high quality name brands. on the issue of hydrogen embrittlement if you buy non plated bolts you can have them plated by a plater that knows what he is doing , preferably someone who does aircraft plating and he will properly bake them after plating to remove the problem of embrittlement all i know is how little i know but the guy who taught me was crew chief on denny hulmes mcclaren M20 canam car while it was being raced in the european interseries and that car has tons of grade 8. further and probably more important in my opinion is installing bolts with proper grip length, regards ,jerry

[blykins]

Guys....

I've researched a little bit since the post started earlier. I was kinda confused about some comments that Dan Case made. He made the comment that Grade 8 bolts were more brittle than Grade 5....and that Grade 5 bolts would just plastically deform rather than suddenly fail.

I took his post, but didn't really put much thought into it at the time....knowing the fact that materials can be worked in different ways, giving them different properties and failure modes.

However since then, I've found some interesting facts....

Grade 5 bolt = 120000 psi TS (tensile strength), 75000 psi SS (shear strength), Rockwell Hardness C25-C34.

Grade 8 bolt = 150000 psi TS, 91000 psi SS, RH C33-C39.

Now everyone knows that there are tolerances when manufacturing takes place. But given that you have one of each Grade bolt and they each spec out perfectly to their design specs, then there is only one way to rule this one....

Grade 8 is superior overall.

It will take 30000 psi more in tensile stress and 16000 psi more in shear stress. That's a lot.

Tensile strength pertains to the bolt being pulled axially (fixed on each end, trying to pull it apart) or it could pertain to the bolt being bent.

Shear strength could be taken in two ways....vertical shear (similar to laying a log down and chopping it with an axe) and torsional shear (grabbing a piece of round metal and twisting each end in opposite direction).

I saw that Grade 5 stuff is made from mild steel. Grade 8 is made from mild alloy steel. That's why Grade 8 is a little harder.

Which one to use? To answer that question for each part of the car, you would have to do a statics analysis and fatigue stress test for each scenario. Some studies would probably show that a Grade 8 bolt would be overkill.....

But this is how I look at it....What does a bolt do? It essentially clamps two pieces of metal together and holds it. You have the head of the bolt pulling the fastener in one direction and you have the nut pulling the other direction. This is axial tensile stress. Unless you do a study on your application and find the tensile stress is not that high, then I would overkill the situation. Better safe than sorry.

Why do some manufacturers use G5 stuff over G8? Because the loads are not that great...and it's cheaper.

Even if it were the case that a G8 bolt would just fail all of a sudden while a G5 bolt slowly plastically deformed.....I would still want the G8 bolt. Why? Because of the tensile strengths of each fastener. The G5 bolt would be already deformed and stretched out 30ksi earlier.....The G8 bolt would still be going strong in its original shape at that point.

[RedBarchetta]

Dave, sorry didn't see your thread when I opened mine. We both had the same idea.

-Dean

[Brent Mills]

Threads merged...This thread now starts with Don's posts.

[CobraCooter]

I am a mechanical designer of heavy industrial machinery. I think the most important thing that is being overlooked here is the critical necessity of properly torqing fasteners that are heavily loaded.

Gr. 8 fasteners and higher design properties are achieved only when they have been torqued or preloaded to the specified levels. Gr. 8 hardware does not perform and may experience premature or outright catastrophic failure if un torqued.

As Gr. 5 hardware has a much lower yield to ultimate ratio than gr.8 it is more forgiving and is used for general assembly. And I hate to be a bubble buster here but if the components in our cars were really under such heavy loads and subject to very high service factors then there would not be a fastener under 1/2-13 and 3/4, 7/8, and larger would be the norm.

Car companies are not in the business of putting peoples lives in danger and try their best to get a vehicle past the warranty stage.

My two sense anyways.

Mark

[jerryweichers]

cobracooter, ok since mr e. wood has stated that i am a moron. please enlighten me as you seem to have the credentials what is wrong with my approach . i use only grade 8 nat. fine or better ie aircraft. fit every thing for grip length. an washers under head and nut, torque using an nylocks unless the application will be subject to heat,then i use an locking nuts when i am finished with the car i put a few miles on it then nut and bolt the entire car retorque every thing , rebleed the brakes using dot 4, change all fluids and then enjoy . while building the car i have all suspension crack checked any plating is done by platers that do aircraft work so they know how to bake the part to take care of hydrogen imbrittlement, i deburr every hole ,dress every panel first with file then , sand even if the panel is edged with rubber and will never be seen . these cars if run with 427's and bronze bushings produce a lot of vibration and need to be properly looked after in my opinion so no amount of attention to detail is overkill . i would also value your opinion on forging vs billet alluminumvs fabricated tubuler steel considering proper build quality for critical suspension pieces thankyou in advance for your help, jerry

[Dan Case]

Off Shore Hardware
Whatever hardware grade you calculate or decide to use, make sure you know where it comes from.

I work for one of the world’s largest companies. Our manufacturing plant is one of my employer’s largest sites. To stay competitive price wise we much source materials and parts from off shore. We get maybe (guess) 20% of our materials and parts off shore. The off shore suppliers are capable of producing materials and parts to American and ISO specifications but our experience is they do it only if you police them rigorously. We have our own engineering department at our plant. They tell me they spend 90% of their time trying to enforce the specifications set forth in our drawings and engineering files. Steel products properties of all types are the toughest to get off shore manufacturers to comply with. Example: We have one particular specialty screw, a type of sheet metal screw made to fit our exact application, that our plant uses more than a quarter of a million of a week. A quarter of a million of one part a week is a pretty good account for a fastener salesperson. We have used several of the largest American producers to supply this part with little problem. An off shore company offered to make them to our specifications. Our engineers tried several lots from the off shore folks and they would not work, their threads pealed off most of the time. We could not use them so we are still with an American supplier. The off shore folks had little to loose if we don’t like their product. The American company does.

I encourage you to buy fasteners from a supply company that specializes in such products; the local lumber yard that also sells bolts does not qualify. Top fastener supply houses can also offer some help in fastener selection. The big brand name fastener manufacturer companies all have websites and have contact information for asking for help.

[ItBites]

Jerry,

My problem with your posting was that you indicated there is something wrong with grade5 bolts, just because they are grade5. Your assertion was that there is no place for grade5 and if you get a car with grade5 on it, it must be changed. This thinking is not only incorrect, it displays a general lack of knowledge in fastener design. Maybe moron was too strong.

There is nothing wrong with using grade8 anywhere you don't need an even better fastener, like an unbrako. some places, such as cranks and rods and heads need better than grade8, but I suspect you knew that and were generalizing.

It is also true that in many locations, a grade5 fastener is acceptable and safe. It just depends on the loading. This is where I had difficulty with your assertion that all grade5s are dangerous and must be changed to grade8. For example, grade5s are ok for valve cover bolts, where your torque limits the fastener load anyway...

If you like grade8 better in ALL locations that is fine, but just don't go telling everyone that it has to be that way or the car is dangerous unless you've run the appropriate calculations to back up your assertion.

It is true many car builders build fine cars without this skill (you may fall into this category), but to build something superlight, strong and fast, like an indy car, you need to actually engineer it, rather than seat of the pants.

If you'd have expressed your opinion that it is better to use grade8 where you can, then fine, but you had the nerve to tell folks their cars are dangerous if they use grade5 anywhere. You simply cannot justify that statement as it is not fact. Some cars may be dabgerous, some may be just fine.

You have to admit you are not a trained expert in this matter. You can express your opinion, but it its no more than that.

If youd like to learn more it has been suggested that Unbrako fasteners have a pretty good explanation. Unbrakos are likely the best fasteners in the world and they know their stuff.

I know a little as well and have developed standards for aerospace companies and have defined acceptable policies for NASA from time to time. PM me and I'll let you know my credentials, just be sure to let me know yours as well.

Have a nice day

[mrmustang]

Jerry,

Let's face it, your up 18+ hours a day posting on this board (and how many others), the same basic thing over and over and over. If you have something to add that is on topic to this thread, then do so by all means......Otherwise.......Your obsessed, and not in a positive way. I wish you would take my initial advice and take a giant step away from the computer for the rest of the holiday weekend. Spend your time with your family and friends and forget all about this forum, your KMP issues, and anything else that winds you up in a negative way. If you allow it to consume you further, you will do yourself more harm than good.

I do hope you find this helpful, as it is meant to be.

Sincerely,

Bill S.

[John McMahon]

Really Jerry,

Are you here to say anything?

Get over the moron comment, I've been called worse here.

The path that has led you to this point, was one of your own choosing.

"Shoulda, Woulda, Coulda"...but you didn't.

Love and kisses,

John

"King of the Idiots"
"Lord of the JOs"
"Prince of the Enema Bag"
"Sir Loin of Beef, Quadrant of Ten, Milk of Magnesia"

[Byots]

nm .

[computerworks]

Mod Note...

...swept up a bit in this thread and combined other thread/posts on the same topic into this one.

This thread will be monitored closely to keep it on topic.
Side trips and personal posts, from here on, will be deleted.

Many of us think that this discussion on bolts and fasteners is a very important and interesting topic and the input from members expert in this area is a valuable commodity.

Thanks
Ron
ClubCobra Moderator

[CowtownCobra]

Could someone list a good supplier for high grade racing fasteners

[Specialk]

Dave,

I get everything from Fastenal www.fastenal.com . The only problem with buying from them is you must buy a package. That means if you need three 5/16 X 4" bolts, you need to buy 10. Small price to pay for quality fasteners.

They probably have a store near you.

[Dan Case]

Quote:

”I've researched a little bit since the post started earlier. I was kinda confused about some comments that Dan Case made. He made the comment that Grade 8 bolts were more brittle than Grade 5....and that Grade 5 bolts would just plastically deform rather than suddenly fail.”

blykins

Response:

The typical steel grades and heat treatments used for Grade 5 type bolts will allow significant deformation before breakage in almost all cases. An assembly might get so loose as to rattle long before the bolt(s) breaks. My experience, mostly at work in very vertical (we buy hundreds of millions of pounds of raw materials and ship finished goods) manufacturing operation, is that the first sign of a Grade 8 bolt problem is its head laying in the isle and we have to figure out where it came from. I have found original British bolts (I don’t know what how they would classify but most are low hardness.) in Cobras I have worked on stretched over 1/16” but they were still keeping the car together. In what I have read under OEM websites you are better off having a lets say Grade 5 bolt torqued to 80% of its yield strength than a Grade 8 bolt tighten to anything less than 80% of its strength. I doubt you could tighten many Grade 8 bolts to 80% of their strength if you were holding two annealed cold finished steel parts together without damaging the parts you are trying to keep together. I have not tested every type fastener and material in an original Cobra but I have tested quite a few and there are few hardened parts in an original Cobra chassis I have found so far. I have also had to repair quite a few Cobra chassis parts that somebody damaged by under and over tightening fasteners. Since there is no place you can go buy exact dimension, look, and performance parts for original Cobras I reverse engineer and have made what I need. Part of doing so includes actually measuring the Rockwell hardness of original parts and research what the transportation/automotive industry would use in that type application and how they would process it into a finished part.

Unfortunately you can not cover everything in a simple fashion. Properties of Rockwell hardness, tensile, yield, and elongation is not the only ones that determine how a part will behave. The process used to produce the steel and the processes to make the part are also major players.
Example 1:

We have one device used to manufacture product that is a type of threaded valve stem. In 1973 when the device was first designed the engineers searched the world over for a commercial material and tool shop to fit the need. Early materials tried failed, i.e. parts snapped off at the first thread, within a day or two of use. Bear in mind they were doing this with full co-operation of the steel companies they were working with. It took two years of development to find a “steel” and a “process” to make parts that would last their desired design life. The application is one of the most severe I have ever encountered. A steel company was found that had a specialty tool steel that technically was an AISI “standard” material based only on the ingredients it contained. Their secret was in producing a grain structure no one else knew how to do. Fast forward from 1975 to 1989. In 1989 we started have sudden early breakage again. Failure analyses were done by the steel company and the world’s largest independent failure analysis company. What was wrong? The grain structure of the “new” material was nowhere close to the “old” material. We use the parts at a Rockwell C scale hardness of nearly 60. That is hard. The material also has an extremely high tensile strength. The old material would withstand bending and impact, the new would not. NEW AND OLD TESTED AS HAVING THE SAME ROCKWELL HARDNESS, SAME TENSILE STRENGTH, AND SAME CHEMISTRY. Their respective performances are worlds apart! What changed? The original company bought out another steel company and stopped making the steel themselves. The original company made 30 ton heats of material, processed it, and held it in inventory until somebody ordered it all. The new mill made 3 ton heats only after enough orders came in. Steel makers will tell you there is a world of difference in making tool steels in 30 ton versus 3 ton heats; you will not get the same properties. The steel company was totally unwilling to do anything to improve the performance. We selected a patented process material from another steel maker that is as far as AISI is concerned almost exactly the same steel and have had zero failures in years.

Example 2:
We use many millions of pounds of various cold finished low carbon steels a year. All are purchased to industry specifications and tested per ASTM methods. No two steel mills make large run commercial materials to a given specification that performs the exact same way except by random chance. This includes two mills from one company. They produce materials that fall into a range of chemistries and performance. This causes us endless trial runs to figure out how to use what purchasing bought. Steel purchased from a supplier from two of its mills can be night a day different. This is partly because industry standards are so broad but mostly due to equipment designs. Steel made the same day by the same company two states apart may vary in yield by 20% mostly because of the type equipment used at the separate mills. The steel companies could make the steels the same at all mills but nobody would want to pay their price for doing so. Even one mill will only typically guarantee a yield lot to lot within a range of 10% unless you want to pay a lot extra. Our plant has to deal with this constantly. That is part of my job.

Going back to my first 2 cents. Bolt grades are performance criteria and not necessarily anything to do with which AISI/SAE steel gets used, although more complex alloys are required to get higher tensile performance. Higher carbon content/complex alloys to get hardness and tensile up generally trade off with lower resistance to fatigue stresses in bending or impact. Pick up any steel supplier’s catalog and it will have some charts that show the trade offs of strength in tensile, wear, impact, fatigue, etc. among products. The higher the final hardness the less likely the material can stand anything but pure tensile or pure compression. A pot hole in the road is not likely to increase tensile load on components a lot but depending on what supports what connects to what some parts could be side loaded a lot. The Cobra control arm bent two plus inches I took off once sure wasn’t in tensile or compression. (The control arm bolts were bent too but they did not break. I bet you didn’t know there was such a thing possible as a 289 Cobra with a 90” wheel base on one side and 87” on the other after it had been restored!) Anybody could buy the “same grade” steel in name only as the big companies use and sell bolts saying they are made with the right material but that does not mean they meet the performance requirements. Counterfeiting of name brand top of the line fastener products with inferior material and processes is a very big business out there in the dog eat dog world. Just because the fastener has the grade markings don’t mean it is what is says it is.

Whatever you use, be sure it comes from a reputable supplier.

[blykins]

Byots.....are you talking about strain? Strain is % elongation.....the same thing that engine builders use to torque rod bolts.....they measure the strain, or % elongation to calculate how much torque is on the fastener.

[mikiec]

An additional question about bolts...

What is the difference between a fine thread and coarse thread?

Mike

[Byots]

nm .

[ToyCollector]

Great thread. I did some reading on ARP's site and offer up some neat links discussing metal grades, aircraft grade vs others, etc. ARP has very strong sentiments AGAINST using aircraft grade bolts in critical applications.

http://www.arp-bolts.com/pages/tech/fastener.html

http://www.arp-bolts.com/pages/tech/matspec.html

[Rick Parker]

Here is a supplier that is well thought of in the racing commuinty. They have a good bolt selection in AN sizes for both shear and tension applications.
One thing that has not been mentioned is the diameter of a typical grade 5 or 8 bolt can be off size by several thousandths of an inch allowing for a loose fit in a drilled hole. Whereas a AN bolt is more closely sized to a coresponding hole size for a much better fit. You wont see and Grade 8 stuff on a real "Race Car".

http://www.pegasusautoracing.com/adv...oryID=HARDWARE

Rick