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Discussion Starter · #1 ·
This is probably a dumb question but I can't find an answer via Google or my fastener bible (Nuts, Bolts, Fasteners, and Plumbing Handbook by Carroll Smith).

Is there any difference between a Grade 8 fastener and a hardened Grade 8 fastener?

Several fasteners that I've seen labeled as hardened Grade 8 don't have the cadmium plating on them while a "normal" Grade 8 does have the plating. Other than the presence/absence of plating/coating is there any strength difference? I always thought that a Grade 8 was a Grade 8 was a Grade 8 (unless counterfeit of course).

Thanks,

Mike
 

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Grade 8

Mike:

Grade 8 is grade 8. Some advertising will state "hardened grade 8" which just describes what a grade 8 bolt is specified at. ie. hardened. Plated bolts just resist rust and corrosion better. Since cadmium plating was basically banned because of the health risks, a zinc allow is used that has a yellowish/golden look to it.

Grade 8 bolts are surface hardened to make them stronger in tension terms, but they are a little more brittle in shear. For most automotive uses grade 5 bolts are fine. Some applications need grade 8 where you want to make a smaller bolt do the job of a bigger bolt. Flywheel bolts and rod bolts are a good example. See the chart to get an idea of the relative strength. A single 7/16 inch grade 5 bolt will hold up your whole car for instance.

https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

Ron
 

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The number Grade Designation is an SAE (Society of Automotive Engineers) Standard; SAE J429d is what is in my 1969 SAE handbook. This standard covers the mechanical and quality requirements for steel bolts, screws and studs. This standard calls out a min. Tensile Strength of 150,000 psi for a Grade 8 bolt and a Min. hardness of 302 and a Max. hardness of 352 on the Brinell scale. If a fastener doesn’t meet these criteria it’s not a Grade 8. SAE specifies the fastener geometry, heat treat criteria as well as testing procedure. Plating does not enter in to grade designation. That’s another SAE standard.

Jack
 

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Discussion Starter · #4 ·
Good...that's what I thought.

So, a $9 "hardened" Grade 8 bolt from the stealership is the same as a regular $1.00 Grade 8 bolt from Fastenal or some other reputable supplier.

I was 99% sure, but, why not ask the question to be 100% sure. These are critical bolts after all.
 

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Yeah

Good...that's what I thought.

So, a $9 "hardened" Grade 8 bolt from the stealership is the same as a regular $1.00 Grade 8 bolt from Fastenal or some other reputable supplier.

I was 99% sure, but, why not ask the question to be 100% sure. These are critical bolts after all.
Mike: Except when the following applies. 1. The bolt is specially designed for some specific application so it has a special length that an off the shelf bolt doesn't have, (ie. too long or too short). 2. It has a special shank like a flywheel bolt for instance. 3. Brake caliper flanged bolts with the right shank from the manufacturer are usually the best choice for that app.

Ron
 

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There are differences in fasteners even within grades otherwise companies such as ARP would not exist. I think that for the most part common fasteners are OK to use but if there is something that I am either betting a lot of money on such as highly stressed engine fasteners or that I am betting my life on such as suspension fasteners, I will spend the extra money for a good quality fastener. There is some good information about fasteners in the link below the body of this post, notice the differences in fastener strength for the same grades in the table. One thing I do not agree with is installing a dry fastener. ARP for instance requires a decrease in torque by percentage when using their fastener lubricant.

http://www.healey6.com/Technical/Bolt Grades.pdf
 

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Mike: Except when the following applies. 1. The bolt is specially designed for some specific application so it has a special length that an off the shelf bolt doesn't have, (ie. too long or too short). 2. It has a special shank like a flywheel bolt for instance. 3. Brake caliper flanged bolts with the right shank from the manufacturer are usually the best choice for that app.

Ron
4. They are made in China :w00t:
 
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