Quote Originally Posted by Flee View Post
4.8 - Stay far away (actually 4.6 mild steel)
8.8 - lower end of higj tensile. (Typical HT bolt)
10.9 - propper high tensile. (Also known as stretch bolts, or torque to yield bolts. Great for keeping a constant torque, cylinder head bolts are 10.9)
12.1 - really hard high tensile. (Great tensile strength, but terrible shear strength.)
Allan caps are equivalent to 10.9. (No, you get Allen caps in all grades from 8.8.)
Stainless bolts are about 8.8 plus. (Disagree, SS bolts are usually around 6, depending on SS grade)

I recommend 10.9, high tensile but not too hard, has a really good uts for our application. (Will be fine, but the shear strength is not as good as 8.8. Much more brittle.)
Note; always torque ht bolts, only use once! If you loosen tjem afterwards discard.

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