Grade 5 vs Grade 8 bolts

[Tom Valet]

This question came up over on the Cobra build forum---what grade bolts to use as replacement on a suspension piece. A big debate then ensued with many people suggesting that Grade 8 is always superior to Grade 5 in every application, in short that is a superior bolt and the only reason to use grade 5 would be for lower cost where higher strength is not needed.

http://www.ffcobra.com/forums/showthread.php?t=212233

Are there any applications on a race car where one would not use grade 8 because of its brittleness? Are grade 8 bolts more likely to fracture rather than bend?

Thanks

Tom

[Marshall Mauney]

Better solution: Use AN and don't worry about whether the "Grade 5" or "Grade 8" you get from the hardware store is really made to the proper specs. Seriously.

[johnd]

Tom:

We shoud talk.

Gr 5, 120KSI min tensile. Gr 8, 150KSI min. Gr 5 hardness, Rc25-34. Gr 8, hardness Rc33-39.

In general AN bolts, or Gr8 will fulfil most if not all applications we run into. There is a trade off between ductility and tensile (hardness). About the only place where I could think to want something more ductile than hard, would be in applications where bending would be preferred as the initial failure mode over fracture.

In practice I do prefer to find AN hardware, not specifically for hardness, but for what I perceive to be better overall quality (thread form, shank diameter controls, and shank to head radius rolling).


John D.

[formulasuper]

I use AN (Army Navy) or MS (Military Standard) hardware everywhere I can. Us in the aviation industry don't like to take chances with hardware.

[rv greg]

I always use AN on suspension parts because you know for sure the quality. The grade 5, 8 you get from the hardware store are mostly made in China and you know what crap they make.
Greg

[RobLav]

I try to use AN - certainly in suspension components. Grade 8 works in some areas, but I prefer the larger diameter AN - less slop. I also use some MS hardware in a few spots - like jetnuts and tension bolts (even larger diameter) in shock and bell crank mounts.

[Rick Ross]

AN/MS is best, but Grade 8 is sufficient for almost all applications on these types of cars. I would stay away from Grade 5 except for non-critical applications.

[D.T. Benner]

Most modern Formula and Sports Racer cars use some very small dia. bolts in high load areas. I have had Mil. Spec. Bolts deformed in spectacular ways from "Racing Incidents" but not to many ever Failed.
In a big heavy car they can use lower grade bolts as the weight of a larger bolt is not much of an issue. Maybe a large lower grade bolt is OK in those applications.

[Daryl DeArman]

Are there any applications on a race car where one would not use grade 8 because of its brittleness? Are grade 8 bolts more likely to fracture rather than bend?

I was advised by those with opinions' I respect to change the motor mount to chassis bolts on my Crossle 32 to grade 5 after I had a grade 8 bolt shear underneath the head. All of my suspension, brake and steering hardware was AN.

[Rick Iverson]

Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook reads something to the effect "if they don't use grade 5 bolts on airplanes, why would I use them on my racecars?"

Tom, if you do not have this book and for no other reason, buy it for some light reading. It will soon become a centerpiece in your library. He was an amazing man.

Iverson

Post Scriptum - I am in agreement with everyone else regarding AN/MS. Shop around and you'll find bargains are abundant.

[rmccown]

I was going to say use AN/MS and not worry about hardware store quality, but I see it has already been covered.

[DB4 Tim]

All his books seem to have great "stuff" in them.

Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook reads something to the effect "if they don't use grade 5 bolts on airplanes, why would I use them on my racecars?"

Tom, if you do not have this book and for no other reason, buy it for some light reading. It will soon become a centerpiece in your library. He was an amazing man.

Iverson

Post Scriptum - I am in agreement with everyone else regarding AN/MS. Shop around and you'll find bargains are abundant.

[ghickman]

Something else that I see wasn't covered in this post is "GRIP LENGTH". Typical hardware store bolts in both GR5 & GR8 are either threaded up to the head or depending on bolt length have very long threads. This doesn't allow proper use of UNTHREADED portion of the bolt.

If you plan to use AN or MS hardware get yourself a thread measuring gauge. Most aviation supply houses sell them fairly cheap. Once you get a grasp of how AN & MS bolts are sized it makes ordering much simpler. Just remember when using them on suspension pickups in double shear select a grip length that keeps any of the thread out of the load bearing area....this really is a good practice on any application.

GH

[rmccown]

Carroll Smith's Nuts, Bolts, Fasteners, and Plumbing Handbook reads something to the effect "if they don't use grade 5 bolts on airplanes, why would I use them on my racecars?"

Tom, if you do not have this book and for no other reason, buy it for some light reading. It will soon become a centerpiece in your library. He was an amazing man.

Iverson

Post Scriptum - I am in agreement with everyone else regarding AN/MS. Shop around and you'll find bargains are abundant.

I have this book on my nightstand. Its a great one to just browse through for "Oh, I didnt know why they did that" information.

It also has been pointing out things about my car that I need to fix. (single vs double shear)

[SWMyers]

I was advised by those with opinions' I respect to change the motor mount to chassis bolts on my Crossle 32 to grade 5 after I had a grade 8 bolt shear underneath the head. All of my suspension, brake and steering hardware was AN.

I second this approach. I use grade 5 (or metric grade 8.8) in motor mounts and anything where being screwed into a tapped casting. As you said, higher grades tend to snap.

[sracing]

Go AN.

BTW, We have most all AN hardware in stock. Not all is listed on the web site yet, but we probably have it in stock. (At good pricing.)

http://sracing.com/Store/Hardware_Ch...N_hardware.htm

Jim

[Matt King]

AN is great. Until you need a bolt on a Sunday afternoon!

[sracing]

AN is great. Until you need a bolt on a Sunday afternoon!

For $50 to $100 you can carry a spare of every AN piece of hardware on your car in the trailer. It's a good idea.

[Matt King]

And for about $8000 I could carry a spare of every part in my car and never worry about missing a session.

[HNR Engineer]

What is just as important as the grade bolt you use is that you TORQUE it up to the correct torque for the application or bolt size (application being prefered).

Lower grades might need re-torquing due to them stretching/elongation if the torque is high for that grade so check what is allowable for that grade.

If your bolt has the incorrect torque (too low for example) for the size or application it will cycle through and eventually fail to fatigue (by shear, bending or whatever cyclic stress) no matter what the grade.

You can do a google search for the tables or refer to many manuals that will provide this information.

[Tom Valet]

Thanks for all the replies and helpful advice. Fortunately, we have not yet had any bolt failures that have caused an accident, so I hadnt given much thought to replacement bolts. The thread on the Cobra forum got me thinking, since there were so many divergent opinions there, most of them by good meaning but probably uninformed people. I figured I would check here for the proper advice.

AN it is !

Thanks

Tom

PS, another question if you dont mind--is there a useful life span for typical suspension AN bolts on our formula cars? Do they need regular replacement as part of usual preventive maintenance?

[Chris Robson]

I use AN and MA spec on everything, including my girls Quarter Midgets. This raised quite a few eyebrows and a lively discussion. My point was that I wanted to have my daughters have the safest vehicles possible and that I thought this is a relativity inexpensive way to provide safety and prevent unnecessary failure. The rebuttal I received was that most cars would "only" suffer one or two bolt failures during the year!....

My reply was huh!?!....
...and I quietly walked away, hoping their one (or two) a year failure was not in front of us!

Chris Robson

[Daryl DeArman]

What AN fastener are you guys using in motor mount applications? Perhaps I was under the wrong impression that all AN bolts were fine thread and of a thread length proportional to their diameter.

In short, no Grade8 anywhere on the car. AN/MS everywhere possible and Grade 5 where it isn't.

[Brian]

Bolts is a subject I've studied for years. It's all about what you are doing with it. AN and other Milspec bolts are not all that great for tension applications. They are lousy for blind thead into aluminium or magnesium casting applications, since they are only commonly around in fine thread, and the thread length is too short. AN bolts aren't all that strong at 125K psi (in tension), pretty much the same as Grade 5. Grade 8 is about 150K psi (going from memory, too lazy on a Sunday afternoon to look up the actual spec) and socket headed cap screws from places like Allen and Holokrome are 180K psi. You can use a SHCS as a rod bolt in a pinch and it will do a good job. SAE and most SHCS's aren't rated in shear. A good bolt for high strength tension applications is L9, which isn't a "grade", it's a commercial name. There is no such thing as a "Grade 9" fastener, in SAE rating. There are tons of higher quality fasteners around, like the race oriented ones from ARP, and various Milspec ratings. I was looking for some good rod bolts for an odd application one time and found a 320K psi bolt in the right size, for a Rolls Royce jet engine, that only cost $300 each in qty 10 or less....

I personally don't use AN or Milspec bolts unless the application calls for it. I do know how to calculate loads and strengths to find that out, though. AN bolts are specified and designed for shear applications, which is why they come in so many sizes and with such a short threaded length. I use Grade 8 for virtually everything except where I use Milspec higher than AN. I do buy my Grade 8 bolts (which often have better plating than Milspec bolts, for some reason) from a high quality manufacturer who makes them in Canada, not China. I won't, for example, buy fasteners from Fastenal, I've had absolute crap from them. I buy my fasteners from Brafasco or Spaenaur, or from aircraft supply places.

If anyone knows a distributor of cad plated Holokrome SHCS's, I'd appreciate it. I was using them for almost everything and my supplier stopped carrying them. I'm looking for decent pricing on 50 - 100 qty of various sizes.

Cheers, brian

[TimW]

PS, another question if you dont mind--is there a useful life span for typical suspension AN bolts on our formula cars? Do they need regular replacement as part of usual preventive maintenance?

I replaced every single bolt when I converted the car; nothing was reused. I replace every safety critical bolt when the engine goes out for rebuild (suspension bolts, toe link bolts, etc.). Its less that $150 to do all the key AN bolts on the car.

What AN fastener are you guys using in motor mount applications?

http://gen-aircraft-hardware.com/ima...ms20073_74.pdf

[ghoneycutt]

just a reminder that a metric bolt marked "8.8" is roughly compared to a grade 5 bolt.
SAE Grade 8 is approximately equal to Metric Class 10.9.

[Daryl DeArman]

http://gen-aircraft-hardware.com/ima...ms20073_74.pdf

Thanks Tim.

I see the MS stuff is available in coarse thread as well, but the thread length is proportional to the diameter. So, with a 5/16" diameter bolt you get about 1/2" of thread regardless of grip or bolt length.

[Brian]

The whole point of AN bolts is that they are designed to be used in a shear application with a nut on the other end. The length is designed so that by selecting the grip length you can have a bolt in double shear with a washer under the head, under the nut, and the unthreaded shank is in the joint acting in shear. The washers come in two thicknesses so that you can always find the right length.

It's interesting that in a bolted joint, the tension from tightening the fastener is taken up in the first five threads of the joint. More threads are superfluous. that's why nuts are as thick as they are. This falls down when the material that the bolt is threaded into is less strong or more ductile than a nut, such as cast iron or any aluminium, etc. There, the threads in the hole tend to distort more easily, and so there is value to having a longer threaded end on a tension bolt.

Higher strength Milspec bolts often have an aggressive radius under the head. You need to accommodate this with the proper washer, an MS20002 which has a countersunk side. The normal AN washers (which I use a ton of) are soft and are not designed to be used in tension applications - they squish out and the bolt loses tension and the joint fails. The MS20002 series is hardened for use in tension applications but it's a bit thicker than a normal AN washer.

Brian

[lancer360]

Bolts is a subject I've studied for years. It's all about what you are doing with it. AN and other Milspec bolts are not all that great for tension applications. They are lousy for blind thead into aluminium or magnesium casting applications, since they are only commonly around in fine thread, and the thread length is too short. AN bolts aren't all that strong at 125K psi (in tension), pretty much the same as Grade 5. Grade 8 is about 150K psi (going from memory, too lazy on a Sunday afternoon to look up the actual spec) and socket headed cap screws from places like Allen and Holokrome are 180K psi. You can use a SHCS as a rod bolt in a pinch and it will do a good job. SAE and most SHCS's aren't rated in shear. A good bolt for high strength tension applications is L9, which isn't a "grade", it's a commercial name. There is no such thing as a "Grade 9" fastener, in SAE rating. There are tons of higher quality fasteners around, like the race oriented ones from ARP, and various Milspec ratings. I was looking for some good rod bolts for an odd application one time and found a 320K psi bolt in the right size, for a Rolls Royce jet engine, that only cost $300 each in qty 10 or less....

I personally don't use AN or Milspec bolts unless the application calls for it. I do know how to calculate loads and strengths to find that out, though. AN bolts are specified and designed for shear applications, which is why they come in so many sizes and with such a short threaded length. I use Grade 8 for virtually everything except where I use Milspec higher than AN. I do buy my Grade 8 bolts (which often have better plating than Milspec bolts, for some reason) from a high quality manufacturer who makes them in Canada, not China. I won't, for example, buy fasteners from Fastenal, I've had absolute crap from them. I buy my fasteners from Brafasco or Spaenaur, or from aircraft supply places.

If anyone knows a distributor of cad plated Holokrome SHCS's, I'd appreciate it. I was using them for almost everything and my supplier stopped carrying them. I'm looking for decent pricing on 50 - 100 qty of various sizes.

Cheers, brian

Great advice! I design bolted joints for a living and fine threads suck in tension. The major draw back to fine threads is that most of the load is carried in the first thread or 2. A courser thread distributes the load more evenly over a larger portion of the threads. This gives much better fatigue loading on a tension bolt compared to a fine thread. As with any joint loaded in tension, the preload on the bolt is critical. This means use a torque wrench and tighten the bolt to the proper setting. Pay very close attention to the torque charts and see if they are for a lubricated bolt or unlubricated. Lubricating a bolt can reduce the necessary torque by as much as 50% depending on the bolt finish and the type of lubricant. Don't guess, look up the torque. It has been shown that a trained mechanic has an accuracy of +/-40% on bolt torque using normal wrenches! A torque wrench brings that down to +/-20%.

AN bolts are great for shear applications. For a properly designed shear joint, high tension in the bolt is not really necessary. If you have a joint that is in tension, socket head cap screws (SHCS) are a good choice. The draw back to SHSC's are the very small head area. If you are using them with aluminum or other softer metal, use a hardened washer under the head to increase the bearing area. Don't use the cheap washers as they often really soft steel. With any bolts that are not AN or you can't get an AN bolt, you are better off buying an ASTM grade bolt from a reputable manufacturer such as Holokrome, such as ASTM F835 which is the specification for SHCS.

[jcorsico]

Bolts is a subject I've studied for years. It's all about what you are doing with it. AN and other Milspec bolts are not all that great for tension applications. They are lousy for blind thead into aluminium or magnesium casting applications, since they are only commonly around in fine thread, and the thread length is too short. AN bolts aren't all that strong at 125K psi (in tension), pretty much the same as Grade 5. Grade 8 is about 150K psi (going from memory, too lazy on a Sunday afternoon to look up the actual spec) and socket headed cap screws from places like Allen and Holokrome are 180K psi. You can use a SHCS as a rod bolt in a pinch and it will do a good job. SAE and most SHCS's aren't rated in shear. A good bolt for high strength tension applications is L9, which isn't a "grade", it's a commercial name. There is no such thing as a "Grade 9" fastener, in SAE rating. There are tons of higher quality fasteners around, like the race oriented ones from ARP, and various Milspec ratings. I was looking for some good rod bolts for an odd application one time and found a 320K psi bolt in the right size, for a Rolls Royce jet engine, that only cost $300 each in qty 10 or less....

I personally don't use AN or Milspec bolts unless the application calls for it. I do know how to calculate loads and strengths to find that out, though. AN bolts are specified and designed for shear applications, which is why they come in so many sizes and with such a short threaded length. I use Grade 8 for virtually everything except where I use Milspec higher than AN. I do buy my Grade 8 bolts (which often have better plating than Milspec bolts, for some reason) from a high quality manufacturer who makes them in Canada, not China. I won't, for example, buy fasteners from Fastenal, I've had absolute crap from them. I buy my fasteners from Brafasco or Spaenaur, or from aircraft supply places.

If anyone knows a distributor of cad plated Holokrome SHCS's, I'd appreciate it. I was using them for almost everything and my supplier stopped carrying them. I'm looking for decent pricing on 50 - 100 qty of various sizes.

Cheers, brian

MSC stocks both Holokrome and Unbrako. Not sure if they have cad plated specifically, but they have a very large selection. www.mscdirect.com

[T644HU05]

It's simple, with a Mil-spec bolt (AN, MS, NAS) you know you are getting a quality bolt made to specific tolerances with specific metals. With your local ACE, Lowes, Billy Bob hardware bolt you're getting a very questionable quality bolt made to the cheapest possible standards. Any store that sells "Chromed" hardware should be avoided for anything other than nails... and those are suspect too.

For metric bolts, wander down to the local wrecking yard and start pulling bolts off of 70's Fiats. Those are among the best metric bolts you'll ever find. Probably well coated in oil too...

[Brian]

It's simple, with a Mil-spec bolt (AN, MS, NAS) you know you are getting a quality bolt made to specific tolerances with specific metals. With your local ACE, Lowes, Billy Bob hardware bolt you're getting a very questionable quality bolt made to the cheapest possible standards. Any store that sells "Chromed" hardware should be avoided for anything other than nails... and those are suspect too.

For metric bolts, wander down to the local wrecking yard and start pulling bolts off of 70's Fiats. Those are among the best metric bolts you'll ever find. Probably well coated in oil too...

Mil-spec are indeed good, but made for a specific purpose which may not be the purpose that you are using it for, that's my point. All the traceability and specific tolerances won't do you any good if the use is incorrect. Non Mil-spec bolts can be just as good quality, just as fine in engineering and production, and may be better suited to the application. Just blindly using the lowest grade of Mil-spec bolt for everything is just as falacious as using Ace is the Place bolts from China. There are steps on the quality continuum in between. For me, just saying "AN" means you're using fairly low grade bolts. Highly specific low grade bolts, but low grade all the same.

Brian

[T644HU05]

Mil-spec are indeed good, but made for a specific purpose which may not be the purpose that you are using it for, that's my point. All the traceability and specific tolerances won't do you any good if the use is incorrect. Non Mil-spec bolts can be just as good quality, just as fine in engineering and production, and may be better suited to the application. Just blindly using the lowest grade of Mil-spec bolt for everything is just as falacious as using Ace is the Place bolts from China. There are steps on the quality continuum in between. For me, just saying "AN" means you're using fairly low grade bolts. Highly specific low grade bolts, but low grade all the same.

Brian

You're the one who screwed an AN bolt into aluminum and/or magnesium in tension!

What I meant to say was I'll use AN, MS and NAS nuts, bolts and washers as designed as opposed to any "Grade-_" nut, bolt or washer because I believe the quality control is much better than the other hardware. What I expect to get shouldn't be in question.

In a past life as a buyer for an airline and having worked aviation parts for almost fifteen years, I never had to change suppliers because I received crap hardware. Untraceable once or twice, but never crap.

[Brian]

Can't argue with no crap!

Brian

[Dennis Valet]

Hate to revive an old thread, but I have a suspension bolt question that applies to my street car.

I recently had a suspension bolt shear on my BMW. The bolt that sheared connects one of the control armors to the spindle. The bolt passes through the control arm bushing and threads into the spindle. There is no nut on the end, it simply gets torqued down and I guess the threads in the spindle hold it in place. (am I even using the right word? Spindle? Mechanic kept calling it a knuckle). The reason I had the shop do the repair is that the sheared bolt was stuck threaded into the spindle and I knew I would screw the spindle up if I tried to remove it. I'm just not that mechanically inclined and don't have the tools for the job.

Anyway, long story short BMW did not have the bolt in stock so my mechanic simply grabbed a grade 8 bolt with the appropriate length, diameter and thread pitch.

I do not know why the original bolt sheared, but given that it did shear, should I be worried about a grade 8 bolt being used in this suspension component? If so, what bolt should I get to replace it?

[DanW]

I doubt the bolt installed is Gr 8, because it is metric. Metric fasteners are usually 8.8, which is roughly equivalent to the US grade 5.

[Tiago Santos]

Yup.. And the metric equivalent to Grade 8 (roughly..) is 10.9 I believe!

[racerdad2]

I would double check with BMW at another shop to be sure you have the correct bolt. EZ to replace now, if need be.

[Dennis Valet]

Thank you.

I guess I should mention that the mechanic did re-thread the spindle to accept the bolt, so it's theoretically possible that he re-threaded it standard instead of metric. Either way I'll get another shop to take a look at it now that the hard work is done and all that would need to be done is replace the bolt.

Thanks guys.

[marshall9]

Something else that I see wasn't covered in this post is "GRIP LENGTH". Typical hardware store bolts in both GR5 & GR8 are either threaded up to the head or depending on bolt length have very long threads. This doesn't allow proper use of UNTHREADED portion of the bolt.

If you plan to use AN or MS hardware get yourself a thread measuring gauge. Most aviation supply houses sell them fairly cheap. Once you get a grasp of how AN & MS bolts are sized it makes ordering much simpler. Just remember when using them on suspension pickups in double shear select a grip length that keeps any of the thread out of the load bearing area....this really is a good practice on any application.

GH

Exactly, grip length often is as important as tensile strength.