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Thread: Grade 8 Vs Stainless?

  1. #1

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    Grade 8 Vs Stainless?

    As I build, replacing everything I can with stainless bolts.

    Question is: Is Stainless = Grade 8 automotive bolts? Would be very happy to replace ALL the fasteners on my truck with stainless hex head for durability and looks. Including chassis, body, and engine (external).

    Just want to make sure the durability is there.

  2. #2


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    Nope SS bolts are only about a grade 2 or 3 they have very low sear strength. Anything that needs to be torqued above 30ft/lbs you should not use SS unless you want to spend $2-$4 a bolt for the high strength SS

    Best thing to do is get nickle plated grade 5 or 8 ( 8.8 or 10+ metric)

  3. #3



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    There are different grade stainless like standard bolts - high strength stainless gets pricy much faster than regular bolts. Unfortunately, it is much harder to find legit high strength bolts of any kind - there are so many counterfeit ones out there. I think there is a chart on here that identifies the markings.
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    i have used stainless in a few places were there is alot of push/pull going on . mainly because they were free . used them on traction bars 3/4 inch and 5/8 have had zero neg results.

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    Not sure if it's worthy, but Most stainless steel is non magnetic too.


    Tensile Strength: The maximum load in tension (pulling apart) which a material can withstand before breaking or fracturing.
    Yield Strength: The maximum load at which a material exhibits a specific permanent deformation
    Proof Load: An axial tensile load which the product must withstand without evidence of any permanent set.

    1MPa = 1N/mm2 = 145 pounds/inch2

  6. #6



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    One of the big difference between grade 5 and 8 is the elasticity of the bolt.
    Grade 5 has a larger range of stretch VS grade 8. Grade 8 has a smaller range of stretch and shrink. So they will hold better but will snap easier if run out side the designed spec. While a case hardened bolt is harder to break but has less stretch then the grade 8 and is good for things like frame to spring hanger connections but bad for things that get hot and cool off. Stainless is good for things that corrosion is a problem like the header.
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  7. #7

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    Quote Originally Posted by camoit View Post
    One of the big difference between grade 5 and 8 is the elasticity of the bolt.
    Grade 5 has a larger range of stretch VS grade 8. Grade 8 has a smaller range of stretch and shrink. So they will hold better but will snap easier if run out side the designed spec. While a case hardened bolt is harder to break but has less stretch then the grade 8 and is good for things like frame to spring hanger connections but bad for things that get hot and cool off. Stainless is good for things that corrosion is a problem like the header.
    This is mostly true, however you will find if you mix stainless and carbon steel like using stainless bolts on your headers over time they will seize worse than a carbon steel bolt. The two metals react with one another, it gets ugly quick. I just removed a carbon steel gearbox from a stainless shaft. The gearbox had been in place for a little over a year, I had to cut the gearbox off the shaft it was seized so badly. Just something to keep in mind, if you insist on using stainless anti-seize will make your life a lot easier down the road. Anti-seize will also help prevent the bolt from galling when it is tightened.

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