What Is the Shear Strength of a Grade 5 Bolt

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1. Does anyone have any good info on bolt shear strength by grade? I was told while a grade 8 has more resistance to torque, it will break easier in shear than a 5. The basic premise was the higher the torque yield, the harder the bolt and the less ability to flex. Just wondering about bolts in single shear like shock bolts, etc.

2. 5's are more ductile, 8's are more brittle. (+ Strength too)
   Forgiveness of steel, how do I love thee?
   Let me count the 'weighs'...
   The Holochrome slide-selectors (fasteners) of years gone by
   had values for common US screws-bolts by diameter.
   Suspect ARP would have a list on their site.

   Last edited: Sep 10, 2015

3. If you search by structural design + fasteners ( or nuts and bolts) you should find charts on the web the same ones used by structural designers. You should find information on single v double shear, shear strength by diameter and length, grip length and etc.

   I got all that stuff in my structural design books here some place but I am certainly not going to dig them out and tap it in when you can find it yourself.

   I will tell you this in single shear I prefer a grade 5 bolt, but I make no qualms about using a grade 8 bolt in double shear on a car, maybe on a bridge but not on a car. LOL

   To be absolutely correct when selecting a bolt or a structural piece in any design you need to calculate your load factors including live and dead load as well as torque v momentum and etc. Way to much to cover in thread on the HAMB, just introductory was 2 semesters and calculus based physics was required to go any farther in the course of study.

4. AN airframe bolts are superior grade 5, Higher quality are NAS. That being said the problem with todays hardware is you dont where it came from and could test at the lower part of the scale or even below it. luckally most everthing is overbolted and that makes up for it

   
   

5. We do have a tendency to over engineer our hot rods don't we.

   this is good info, when you are buying off shore you are don't know what you got.

6. I know some racers that go thru drilling their bolts to save weight. I laff and say if that saves any weight you could buy them already done and if the strenght isnt affected you are using too big of a bolt anyway. When I was running my sprint car every major bolt had a 9/16 head (6 & 12point) so that I could check every bolt with just 2 wrenchs

7. As noted, there are hundreds, if not thousands, of charts on-line if you search for 'bolt strength'.
   The challenge is sometimes knowing how to read and interpret the information.

   This is one of the many:

   

8. Bob told me that he won't use ARP head studs on his blown fuel hemi. Not good enough. He told me they all use something else that is way stronger. He found one laying on the bench, broken. By internal stress, I guess. Hard to understand how a stronger stud would break like that. Maybe they forgot to draw that one?

9. I used all grade 8's on my hotrod's...probably not the best (see above) but habit. However it wasn't unusual to have tire shake shear the heads off.

10. Years ago I decided that the Big-3 had more money to invest in R&D than I did so it was just easier to follow their example of where to use what-ever grade bolt.
    In my old(er) muscle car days it was ever-so-common to find PS and alternator mounting bolts sheared off in the head or manifold because someone replaced the Gr5 with a Gr8 and the constant vibration caused it to fracture.

    Stronger is not always better unless the application changes.

    .

11. The chart shows fine thread; a 1/4 in dia is 2 tons,
    a 3/8ths is 5 tons. Per fastener!
    Usually issues like fatigue or corrosion & fatigue will sneak up and bite.

12. Like Beaner said we tend to over build which is good. Nice to have that safety factor. If you can find a bolt situation of similar or greater loading in a car than that may be where to start.

    It is odd that a stud failed over bolts in the hemi but there is some root cause. Studs properly sized are usually stronger than bolts. Bolts will fail at the corner of the bolt head to shaft. Bolts are used in flanges on lower pressure piping but high pressure piping codes require studs and nuts for higher strength.

    Whether the threads are in or out of the shear plane makes a difference. The other thing to note is torque values for bolts that are dry or lubricated. A lubricated bolt is easy to over torque so the lubricated torque values are lower. A stud with oil tightened to a dry torque value could be stretched to or close to failure. A dry bolt thread & nut have more friction so a higher torque value given than a lubricated bolt. Care in torquing so it does not fail premature in shear or tension.

    Some bolt info but as Beaner said the fastener topic can get pretty deep. Nice thing with structural steel & piping is one can go to tables for the loading to get bolt up info.
    http://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf

13. Most Big show fuel cars use 9310 tool steel for the head studs and change them often

14. That is probably what Bob told me he is using. 525 inch Hemi with 60 psi boost running for 5 miles. But breaking while laying on the bench would not instill confidence if it was mine.

15. Let me run a bolt issue by someone a lot smarter than me. A while back I had the passenger side, SBC , header flange bolts loosen up on a trip. I ordered grade 8 bolts, locknuts and washers and replaced all six (ps and ds). I was going over the car last month and noticed one bolt was broken but was still in the flange because it was dropped in from the top. I figured with the grade 8 bolts socked up tight it would never cause me to have loose flange bolts again. Any ideas why this bolt failed?

16. How well-supported is everything downstream from the flange? Like it was stated earlier here, harder hardware is not always the answer. You could probably get by with a grade 3 or 5 bolt and a lock nut, or regular nut with Loctite. AND of course, the proper torque.

17. This kind of info is over-interesting to me.....I'm watching this one.

18. A bolt acts somewhat like a spring when tightened, it stretches and stays tightened because the nut/bolt head is under pressure, unable to move due to friction. If it is a part that cycles through high and low temperatures you get thermal expansion that can make it come loose or break bolts.

    If you increase the bolt length that comes under tension by adding extra thick washers or even a piece of tubing (you sometimes see them on exhaust manifold bolts) you get "a longer spring", it can move more before the bolt/nut comes loose or the bolt breaks.

    Feel free to use whatever bolts you want wherever you want them, but DO take a moment to think about if you think you know more than the engineers that designed the engine (or whatever you are working on) first. A higher grade bolt or a bigger size might seem like a good idea alot of the time, but sometimes results are counter intuitive - a softer or smaller bolt may let things move where a stiffer bolt would break or cause something else to break.

19. Agree w/G-son.
    Often a grade 5 will hold up in 'tense' environs, where a more brittle bolt might fail.
    Simply more elastic capacity. (might think of it as stretch)
    There are many aspects to consider, not always an easy problem to address.

20. Several years ago GM had some issues with head bolts breaking on 2.5 litre 4 cyl. engines. The engines were originally assembled, if I remember correctly, with metric 9.8 grade bolts. While strong, they were apparently a bit too brittle. The field fix involved replacing the head bolts with an 8.8 grade version which seemed to cure the problem. either that or they replaced a 10.9 with a 9.8 bolt.

21. The only reason I went with the grade 8 bolts was that I never wanted them to come loose again so with the grade eight I could really sock them up and sure, I could have used grade five and just might. My question is why did one bolt fail. My theory is that I might have tightened them too much and thermal expansion broke it. All the rest are fine, only one popped. I have overkill on exhaust hangers so that's not the issue.

22. Mark's Standard Handbook for Mechanical Engineers lists Grade 5 fasteners as 120 ksi fasteners. This means the tensile strength is 120,000 lbs per square inch. It also lists Grade 8's as 150 ksi fasteners meaning the tensile strength is 150,000 lbs per square inch. Also, the ultimate shear strength of a fastener is typically about 60% of its ultimate tension strength. So given a certain diameter (cross-sectional area) and strength rating, the theoretical capacity of the fastener can be calculated in tension or shear.
    Using a .250-inch diameter grade 8 fastener gives you the following shear capability:

    A = Cross-sectional area of the fastener size (since bolt bodies/shanks have circular cross-sections, use area of a circle) = Pi x r2 where R (radius) = .250/2 = .125, therefore A = Pi x (.125)2 = .0491 square inches (in2)
    Capability in shear = 91,000 lbs / in2 x .0491 in2 = 4468 lbs

    Using the same .250-inch diameter grade 5 fastener results in the following:
    Capability in shear = 75,000 lbs / in2 x .0491 in2 = 3683 lbs

    That's a difference of over 750 lbs or over 1/3 ton. In this example you can clearly see that using a grade 8 fastener has an advantage over the grade 5. This said a grade 5 bolt with a larger cross sectional area will have greater shear strength than a grade 8 with a smaller cross sectional area.
    Large grade 8.....better to stop shear me thinks though I've known hot rodders that can break an anvil with a napkin.

    Larry

23. The problem w/ bolts today, IMO, is the sad fact is, the vast majority are manufactured in China, where quality control is a problem, was in manufacturing all my life and the last 15 or so years, the quality of the brands I purchased for years went in the crapper. Saddly, this true w/ so many things we use today, and before you jump in and tell about, only buy American, I AGREE, but the fact is, not much is made in USA today, A LOT of car parts, big brand names, look at box, made in China. "It is what it is", getting to be a favorite expression on mine.

24. They are spendy because the company is really proud of them but if you want quality bolts hunt down ones made by Lawson. http://www.lawsonproducts.com/
    From what I've seen in in the past most bolts break due to be over tightened beyond their torque specs or because of vibration or having the load pull at an angle rather than at a direct 90 degrees to the bolt.

    p

25. There is no such thing as exhaust header flange bolts that never come loose. What ever bolts you use start loosing up as soon as the flanges get hot the very first time. Then, with every heat cycle, the bolts get softer and stretch more. The best you can hope for is bolts that don't need to be tightened as much. Adding washers (or better yet bell washers) under the bolt heads will buy you more time between tightening cycles, and may actually solve your issues for very long time periods.

    If you really overdid it on the exhaust hangers, that can be contributing to your flange bolt breakage. There has to be enough give in the hangers to allow the pipes to grow longer as they get hot. If the hangers are stiff and heavy duty, that pipe expansion has to go someplace. It will take out the weakest point, which might be your header flange bolts.

    Given the quality of bolts these days, everything I use is now a grade 8. The assumption is with the reduced quality, maybe it will actually be close to a grade 5, which is at least tolerable. Even then i might be fooling myself, but a guy has to do something. Gene

    Last edited: Sep 11, 2015

26. The only 'guarantee' (if such a thing even exists) to keep a cap-screw tight is to use safety wire.
    And Red Locktite will work on exhaust.

    .

27. Grade 8 fasteners have gotten some bad press over the years for their "brittleness". The concern is hydrogen embrittlement due to poor process used in plating - especially zinc plating (chrome plating is even worse). Bolts can be so brittle that the heads pop off when tightened. Worse, yet they can be properly tightened then fail hours or days later due to delayed hydrogen cracking. This problem is cured by using an afterbake in the zinc plating process. The problem is that you can never tell visually if this has been done.

    Simple rule to be 100% safe: don't EVER use Grade 8 fasteners that are zinc or chrome plated unless you're absolutely sure about the process used. Stick to phosphate and oil and live with the lack of corrosion protection

28. we used supertanium on the indy car....

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What Is the Shear Strength of a Grade 5 Bolt

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