for those looking at those amazon fasteners, they are 8.8 metric aka equivalent to grade 5.
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vs SAE
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For those that were told there would be no math, min tensile strength 120,000 psi for grade 5 = 827.3 MPa IE really ******* close to 8.8.
For those that are concerned about torque rating a M8 fastener. A 8.8 fastener is 18.8 ft lbs max. a 10.9 or grade 8 equivalent 26.9 ft lbs. Assuming you didn't put antisieze on it. Read subnotes on K if you did.
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https://www.fastenal.com/content/documents/FastenalTechnicalReferenceGuide.pdf
All tables stolen from above link.
If you don't want to buy the stage 8 stuff ie Bolts Are Aircraft Quality Grade 8– 4130 Alloy Steel. Go to fastenal and pick up proper 10.9 or grade 8 bolts. Since its an M8, I'll bet you its 10.9 your looking for.
https://www.pirate4x4.com/tech/billavista/NutsandBolts/index.html
Also a good read for those with the desire.