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Old 07-18-2006, 08:18 AM
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Grade 8? Grade 5?

Hi all,
Does anybody have any compelling arguments about what to use in frame and chassis applications? Shear and tensile strength of Grade 8 bolts makes me feel that they are best for the application but I've heard arguments that their brittleness proves otherwise. Anybody got $.02??

Cam

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Old 07-18-2006, 11:45 AM
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Grade 5 is not recomended for chassie/ suspension and grade 8 or higher is the only way to go for chassie/ suspension. for metric a 8.8 property # is minimum 10.0 property # is recomended.
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Old 07-18-2006, 08:08 PM
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That is good advice on grade 8 minimum for chassis fasteners. The following is a link to a great (in my opinion) article on Grade 5 vs Grade 8 (and others).

http://www.rockcrawler.com/techrepor...ners/index.asp

I use all Grade 8 fasteners on my T because they are readily available here. I have started to replace chassis/suspension fasteners with mil-spec (MS) fine thread fasteners when the opportunity presents itself. The MS bolts and fasteners have a higher tensile strength than Grade 8 and each bolt diameter can be purchased in a wide array of grip lengths, something that is difficult to do with straight grade 8 fasteners. The MS bolts can also be ordered with drilled heads and/or shanks for safety wire or cotter pins.
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Old 07-18-2006, 08:17 PM
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On chassis and suspension...definately grade 8...fine thread is better too if you can get them.
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Old 07-19-2006, 03:57 PM
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There is only a few cents difference. Why use anything but 8 anywhere. True course thread 8 is harder to find.
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Old 07-19-2006, 04:16 PM
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so where do you get grade 8 bolts? places like home depot have them?
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Old 07-19-2006, 04:34 PM
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Napa, Carquest, Advance auto and the like will have what you need in grade 5 and 8. Home depot will sell probably a lot of grade 5 and a limated supply of grade 8. remember, 6 lines on top is grade 8, 3 is grade 5.
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Old 07-19-2006, 04:59 PM
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A question about the markings. What does the triangle tell me? I have seen it many times on grade 5 and grade 8 bolts.

Thanks

John
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Old 07-19-2006, 05:09 PM
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I belive that is a company marking as it's not mentioned in any of the strength standards that I'm aware of.
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Old 07-19-2006, 07:21 PM
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Might want to look in the yellow pages under Fasteners
Here in SanAntonio there are a couple of places that primarily deal with fasteners.
I work on large printing/bindery equip. and need to get special fasteners on a regular basis.
If you are in a smaller community--McMasterCarr.com--industrial supply
All kinds of neat goodies in there
In general -- any industrial supply may be able to help
Grainger.com

Bryan
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Old 07-19-2006, 07:31 PM
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Tractor Supply sells Grade 8 coarse thread nuts and bolts. About $4 per pound.

Lowe's and Home Depot sell Grade 8, but usually in plastic packets containing 1 or 2 pieces. Expensive way to go - and Lowe's usually charges more for the same fastener.

I buy aircraft grade AN and MS hardware from Wick's Aircraft Supply and Aircraft Spruce & Specialty. Both have web sites - compare prices on the same hardware, I've found significant differences between the two.
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Old 07-20-2006, 06:59 AM
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All good stuff, guys, thanks. i have a little neighborhood Coast to Coast store that's got a killer hardware section. I use them, even though they are a little more expensive. Beats the big warehouse stores hand down.

Cam
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Old 07-21-2006, 12:52 PM
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http://www.fastenal.com/web/home.ex
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Old 07-23-2006, 02:51 PM
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Aircraft is all grade 8 and have ROLLED threads.

"Farm supply/hardware" store stuff has CUT threads.

Also be advised that the bolt's "minor" diameter, the "bolt diameter under the thread groove", is LESS on a course thread than a fine thread, so that even if the bolt is rated at the same shear strength, the tension strength will be less.

Cut threads do increase tendency to crack in tension.

FYI all ARP fasteners are rolled threads.

This is sort of like discussing motorcycle helmets... pro or con.....
well, it is your coconut.

The actor Gary Bussey was adamantly against motorcycle helmets UNTIL he went bouncing down the road without one and almost died.

www.readershotrods.com
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Old 07-23-2006, 09:57 PM
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What Xntrik states is true, however the tension strength issue is really academic, as the bolt, regardless of whether the threads are 'cut' or 'rolled', will still meet the tension carrying specification for the fastener as long as it is torqued correctly, or better yet bolt stretch is measured correctly.

The tension specification for Grade 8 bolts is 150,000 psi minimum failure for fasteners up to 1 inch, and 105,000 psi for larger fasteners. Also, when calculating the tension-carrying limit of the fastener, the minor diameter of the fastener is used to calculate the fastener's inch-squared dimension rather than the diameter of the unthreaded shank. As long as the engineer knows what loads he is dealing with and uses the minor diameter of the fastener to calculate the fastener's inches-squared value, the issue of coarse vs fine should not matter when considering just the tension limit of the fastener.

When the fastener starts to experience tension loads beyond the spec, that is when the issue of coarse / fine, and rolled vs cut threads can make a difference. If the person who engineered the application applies the correctly sized fastener, then these issues should not matter all else being equal.
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