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Posted by: McMark Mar 4 2009, 12:52 PM

Hey guys, I was just reminded about a common misconception that I felt compelled to try and help dispel. It has to do with how fasteners are 'graded'. Often times you will see people talking about high stress joints and people insist on recommending 'Grade 8' bolts. But the fact of the matter is that SAE and Metric bolts are rated differently.

From a thread on TheSamba:

It's quite common for people to go to the hardware store looking for 'Grade 8' metric bolts, see the 8.8 stamping on the head of the bolt, and think they've found the correct part. But the truth is, for high stress joints that require better quality fasteners, our cars need 10.9 bolts, not 'Grade 8'.

Posted by: Vacca Rabite Mar 4 2009, 01:13 PM

You know, I had no idea... Thanks for this post. I need to staple it into my brain.

Zach

Posted by: 6freak Mar 4 2009, 01:33 PM

In my world S.A.E grade 5`s have 3 hash marks and grade 8s have 6....Grade 5`s will stretch before they break giving you a warning ....grade 8`s are brital and just break with no warning ......OSHA requires grade 5`s in all load bearing parts of an overhead crane system ...A325 on the bolt head is also considered a grade 5

Posted by: Solo914 Mar 4 2009, 01:41 PM

, I was writing the same exact thing.

I can't remember though, is it better to have Grade 5 or Grade 8 in shear applications? I distictly remember a cheat sheet for telling you what grade to use in certain applications(shear, tensile, constant load etc)

Kyle

good reading. Pretty much negates what I wrote above.

http://www.rockcrawler.com/techreports/fasteners/index.asp

and

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

Posted by: 6freak Mar 4 2009, 01:56 PM

I myself like 5`s for they can tell you things ...8s are just too brital ..but it really depends on the application..constant loads i would say 8s shear i would take the 5`s ..JMO

Posted by: 6freak Mar 4 2009, 02:08 PM

Just read the rock crawler.com page ...wow .....I learn something new everyday ..but it comes down to this!! what type of application and what do you want to do with it

Posted by: Trav012000 Mar 4 2009, 02:23 PM

Our Chinese Tempering oven here at the factory uses a 4.4 bolt. Needless to say, we've had to replace quite a few bolts.

Posted by: davep Mar 4 2009, 05:12 PM

You also have to consider the size of the bolt. You cannot say I'll replace an ISO 10.9 with a SAE grade 5 because they will stretch and not break. If you do, you may have to go from a M6 bolt to a 1/2" bolt for example.
It is far better to get the exact replacement bolt since some engineer agonized over the selection of it in the first place.

Posted by: MrKona Mar 4 2009, 07:49 PM

I'm confused.

I always replace metric with metric. Does SAE hardware "fit" in place of metric hardware?

Posted by: 6freak Mar 4 2009, 09:21 PM

I agree 100% ..Im basically say`n for bolt on stuff !such as winch bumpers and things like that . the none engineered none load bearing parts ..In some cases SAE will work in place of Metrics... The threads are differant and of course the head size ...but Im with Davep and yourself if you can put origional bolts and nuts in place do so

Posted by: plymouth37 Mar 4 2009, 10:53 PM

Usually not . I was however planning on replacing all of the standard bolts used on my conversion kit with metric bolts. I thought it was stupid to have standard bolts mounting a japanese engine into a german car but what do I know, Renegade only stocked standard so that is what I had to use
Anyway thanks for the info, I was wondering about that.

Posted by: McMark Mar 4 2009, 11:05 PM

I'm not suggesting that SAE and Metric are interchangeable. They're not. But people say, "Go get yourself some M12 grade 8 bolts" which is impossible. They really mean "Go get yourself some M12 grade 10.9 bolts."