Thread: Grade 5 or 8?

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I was reading a thread on the OTHER forum, and it got me wondering what you guys thought. The question was what to use on suspension parts 5 or 8, the guy sayes speedway told him 5 was better for shear factor cause it will bend before breaking, unlike 8 which will snap, so 5 was better in suspension components. Ive always used , and was told to use 8. Now there debating over it, just thought it would be an interesting discussion with all you smart technical fellers around here.

I use Grade 8. I remember the Grade 5 is better story from the circle burner days. Don't know if it's true or not, but I do know I've never broke a Grade 8 that was fastening a suspension piece.....

Grade 8 for suspension... now at 1 time my brother used an unmarked grade 2 bolt to hold the rear strut to the control arm on a VW fox he had.. it didn't break, but that car never ever was quite right, I wouldn't be supprised but what it had streached.

Thats what we used on the lola`s, and the guy that owns the shop has a couple of different engineering degrees, i figured he knew what he was talking about. And ive never heard any stories of them breaking either.

Friend of mine broke a grade 5 he used in the front ladder bar mount... Fortunately it broke coming off the line and not on the big end so there was no other damage done to the car....

It also has something to do with the weight of the car and it's intended usage.... Don't know that using grade 8 on a street cruizer would be essential, but I sure do want them holding the suspension in my race car!!!!!

Whatever grade hardware you use, make sure your supplier is reputable... There's a lot of import counterfit junk on the market these days....Might be stamped as an 8 or a 5, but what is it really????? As with anything, the lowest price is not always the best choice.

Originally Posted by Dave Severson

Friend of mine broke a grade 5 he used in the front ladder bar mount... Fortunately it broke coming off the line and not on the big end so there was no other damage done to the car....

It also has something to do with the weight of the car and it's intended usage.... Don't know that using grade 8 on a street cruizer would be essential, but I sure do want them holding the suspension in my race car!!!!!

Whatever grade hardware you use, make sure your supplier is reputable... There's a lot of import counterfit junk on the market these days....Might be stamped as an 8 or a 5, but what is it really????? As with anything, the lowest price is not always the best choice.

yupp. I only buy Dorman hardware.

I only use Grade 8.....

THIS will explain why.....I hope....

I use grade 8 on everything. I like the color.

However, I notice almost everything we buy, like the Wilwood brakes we just got, have grade 5 inside the box. Evidently the manufacturers feel they are sufficient, but I'm like most of you, I like overkill. (I should never lose a headlight )

Don

We have a Fastenal store in town.... They handle some junk, but they have all the goodies from grade 5 - 9!!!!! Used to have to either order hardware or drive to Sioux Falls (50 miles) to get any kind of selection in grade 8, sure do like having a store right here!

Thanks for the link, Chuck!!! Some really good information there!

The old wives' tale about Grade 8 breaking easier than Grade 5 is just that - a tale, a falsehood, a myth. Kitz - who has much more knowledge in that area than I do commented on it sometime back. Grade 8 is stronger in both tension and shear than grade 5.

Read THIS for more info.

Very informative article Jack.

Don

Originally Posted by Henry Rifle

The old wives' tale about Grade 8 breaking easier than Grade 5 is just that - a tale, a falsehood, a myth. Kitz - who has much more knowledge in that area than I do commented on it sometime back. Grade 8 is stronger in both tension and shear than grade 5.

Read THIS for more info.

Yep, exactly correct.....That's the same article I linked to

Originally Posted by ceh383

Yep, exactly correct.....That's the same article I linked to

Oops. I didn't see the link.

When in doubt, Grade 8.

You can practically design for any fastener you want, just be sure your parts match up with your assumptions and analysis. Or if in doubt, Grade 8.

My Heidts IFS/IRS uses some stainless bolts and nuts which are no better than grade 3 probably. Thing is, they are larger than normal and stress is proportional to area or diameter - squared .............. Oh yeah, and they won't rot out for a long time.

One should never design a fastener to operate beyond its yield point so elongation is usually not as important as strength; = Grade 8.

Kitz

You got that right on the stainless. There are stainless bolts that measure up but you don't even want to know what the price is. Especially if they are big and certified and made in the U.S.A..

As for gr 8. You can't use enough of them. Everthing possible on my car is grade 8.

Last year I found that White Pine is stronger than grade 8 bolts, chrome moly high end rod ends, and 4130 chassis suspension mounts. I made full contact with the tree at 60+ in the sand buggy and removed the left front suspension entirely. No bolts broke, no welds cracked or failed but the 2 of the 4 5/8 rod ends did bust right off leaving the bolts and tabs on the frame. The other 2 rod ends ripped thru the tabs like a sawzall.

I also got to test in real time a 5 point racing harness mounted with gr 8 bolts. The harness survived totally intact like nothing happened. My aging body however took a couple days for the bruises to blossom to full color then another few days to go away. I only remember getting hit like that once back in my tight end days. It just served to remind me that the tighter the belts are the better. Good thing they were tight or I might have found out what impact with the steering wheel feels like.