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Thread: Grade 8 vs. grade 5 bolts

  1. #21
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    grade 12.9 is the metric equivalent of grade 8, its stamped on the head.

    Quote Originally Posted by igotafrigginjeep View Post
    Also, not sure if it would be a Grade 8 if it were a metric thread...but what do I know!?!?!

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    Its like there D-rings that are stamped made in china. If you go to brafasco and buy them they are stamped made in Canada. Why would you try and be cheap on the one things that are important. When your stuck and the only way you are getting unstuck is by getting a tug or winching these are the most important bolts on your vehicle.

    China has this problem with making things with inferior steels or steels that they melt down that are not to the right "specs" (joke) and they sell the steel to other little businesses that believe what they are getting is a quality steel. they manufacture the bolts and sell them here. Nothing is really traceable and everyone believes that they are ok.

    In Canada when you buy steel it comes with tags from the foundry that state what the grade and quantity's of alloying elements/additives and every piece of steel from a mill is numbered and so on. So in the end if something fails the piece of steel can be traced back to where it was made.

    Quote Originally Posted by WranglerIV View Post
    How do you figure ??? Please explain.


  3. #23
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    Isn't Class 10.9 the equivelent?

    Edit: Grade 8: 150,000psi Tensile
    Class 10.9 145,000psi Tensile
    Last edited by JKMotorsports; 08-29-2009 at 01:57 PM.
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  4. #24
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    You are correct, I just took a look at the old bolts from the bumper and they are stamped 10.9. I was looking at charts and they where showing grade 5 and 8 and then they where showing 10.9 and 12.9....you would figure metric would have made a simple 1,2,3 grade system or something.

    Good read from rockcrawler about this subject found here.
    http://www.rockcrawler.com/techrepor...ners/index.asp

    Quote Originally Posted by JKMotorsports View Post
    Isn't Class 10.9 the equivelent?

    Edit: Grade 8: 150,000psi Tensile
    Class 10.9 145,000psi Tensile

  5. #25
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    Quote Originally Posted by biohazard View Post
    be careful with PA stuff, GR8 in china isn't necessarily a GR8 here!!
    unless they take engrish as a second language :rolleyes:

  6. #26
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    Quote Originally Posted by His Royal Jeepness View Post
    " 'never use Grade 8 bolts in any stressed application! There are NO Grade 8s in aircraft, and the FAA does not allow them during its inspection program'! This from someone who was a crewchief for Ford's GT-40 LeMans program, built & ran Indy-cars, NASCAR stockers, formula cars and still runs several, one for his grandson. The idea is, a Grade 5 will deform if overstressed; a Grade 8 will snap.... "
    Let's ignore the fact that this guy makes his qualifications sound like one of those internet spam e-mails and let's just focus on the facts.

    1. My Jeep (unlike the Jeeps of some members on here) doesn't fly. So what's good for the FAA isn't necessarily good for the NHTSA.

    2. Both a Grade 5 and Grade 8 will yield before ultimate failure. The Yield/Tensile limits of Grade 5 are 81/105 and for Grade 8 are 130/150 (all units in KSI, or 1000 psi).

    3. When designing, you usually design around the yield strength. With that said, the Grade 5 bolt has a tensile strength that's almost 30% higher than the yield strength, while the Grade 8 will have a tensile strength that's only 15% above it's yield strength. So his argument does have some merit that the Grade 5 will have more indication. Also, in my unfamiliarity of bolts/fasteners, I am not sure if the yield strength accounts for fatigue (1,000,000+ cycles).

    4. With the aerospace industry, weight is also important. VERY important. The factors of safety aren't as high as they are on passenger vehicles because increasing the factor of safety will always increase the required amount of material, which thus increases your weight. Grade 8 is much stronger (60% yield, 43% tensile) when compared to Grade 5, and that can return a noticeable weight savings.

    5. For any given size, the grade 5 will fail before the grade 8 will even yield.
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  7. #27
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    Much of the above information is correct, more of it is nonsense. Grades of commercially available fasteners and their yield and tensile strengths is easily searched and found on the Internet, I am sure each of you can navigate Google well enough to find it.

    The common commercial hex head capscrews (bolts) are Imperial; Gr2, Gr5 and Gr8 .... Metric; Cl8.8, Cl10.9 and Cl12.9. They all have their own property characteristics and suitable (or non-suitable) applications.

    Bottom line is that while Gr8 or Cl10.9 is normally more than suitable (and desirable) for most applications however ... it is not all the time.

    Understand the what it is that you are fastening together, the stress(s) it will incur, what you require it to achieve to be functional AND safe then pick the correct strength of fastener to perform best in the application. Sometimes it is better for the fastener to fail (not necessarily catastrophic failure meant) first.

    Commercially available fasteners are governed by ANSI, ASTM, IFI and ISO whether they are mfg'd in North America or Offshore. Crabshaver's comment:
    Quote Originally Posted by crabshaver View Post
    .... little does he prolly realize that 90% of generic "off the shelf" fasteners are imported from China and Taiwan.
    is absolutely correct .... yes, even most of Infasco's bolts (identified by the triangle marking on the head) are Chinese or Taiwanese origin. If you have an application where you are really that concerned about getting a "real" Gr8 bolt then buy only those that have a Mfg's/Exporter/Importer head marking (this is not the same as the Radial Lines identifying imperial strength or numerical stamping for Metrics ... these marks are in addition to those). The Mfg/Export/Importer is taking responsibility(liability) for the integrity of the fastener provided it is used in a correct and appropriate application, so if it is "traceability" you are looking for ... there it is.

    Quote Originally Posted by dvsjeep View Post
    Grade 8 is superior to grade 5 in every situation, unless you are looking for the bolt to shear to avoid damage to something else. ( ie shear pin)
    .... absolutely correct but should be edited to include "to shear or deform to avoid damage to something else"
    Last edited by WranglerIV; 09-03-2009 at 12:58 AM.
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  8. #28
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    ^^What you work in the industry or something have a lot of comments on this stuff.

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