Thread: Grade 5 or 8?

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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.

I fully subscribe to the "if in doubt, grade 8" or in my case, ARP's. Even when I pulled my engine apart, all but the rod bolts became ARP's. The only reason they didn't is that I really didn't want to pull the piston and rod assembles. If it ever has to be totally disassembled, then I'll try to find my box of wavy bolts. Every thing load bearing on the chassis is Gr8 or ARP (except some of the chrome fasteners supplied by TCI). Cheap insurance IMHO.

If I were building 500,000 Chevy trucks a year, a bolt that cost 1/10 of one cent less than another would certainly be a factor..... If I am building one car, why not stock one grade and be done with it? Bolts are cheap relative to the amount in a car.... we buy stock from McMaster and keep a Grade 8 bolt rack full. Then, there's never a question.

The old wives tale about a grade 5 vs grade 8 is not true. However, there is high shock tool steel like S7. For bolts, if you're running that close to the edge, you got a bigger problem than the bolt grade.

Gee Bentwings, we really appreciate you going to all that trouble to test the products we use, but there has to be an easier way!! Ever heard of "crash dummies?"

Don

Originally Posted by robot

.... we buy stock from McMaster and keep a Grade 8 bolt rack full. Then, there's never a question.

While McMaster Carr has always been great - I'm starting to see some of their fasteners coming from China. My last months order was kinda surprising as some 1/2-20 nuts were Chinese. They were supposed to be Gr8 but sure were soft (cross threaded one too easily)

Bolt strength is like horsepower:

If somes good

Mores better

and TOO MUCH IS JUST ENOUGH!!!!!!!!!!

I overbuild everything because A I like to be safe and B I'm lazy!

Bolts are graded for strength rather it's a pull or a shear.

Go with the grade 8's

Originally Posted by DennyW

So this makes me wonder then, what grade is the metal that the bolt is holding ?

good ol' hot or cold rolled steel.

The first number is yield strength, the second is ultimate, both in MPal ( or 145.04×10−6 #/sq. in / P):

Structural steel ASTM A36 steel 250 400
Steel, API 5L X65 (Fikret Mert Veral) 448 531
Steel, high strength alloy ASTM A514 690 760
Steel, prestressing strands 1650 1860
Stainless steel AISI 302 - Cold-rolled 520 860
Cast iron 4.5% C, ASTM A-48 130 200
Titanium alloy (6% Al, 4% V) 830 900
Aluminium alloy 2014-T6 400 455

And I have no desire to get my calculator out to figure the difference between the steel and a bolt

Originally Posted by DennyW

I was only wanting people to think about that a minute. You can have a 20 grade bolt, doubt they make that one... but, if the metal can tear and go over the bolt, that is kind of a limiting factor. So if the mating area is equal to the surrounding area, it this good enough ? I know in some areas, they also use the over sized hardened washers to help support the surrounding areas. Just putting some thoughts in it...

Just pickin' on you today, Denny. It's a crappy day and I was just sitting here wondering....... and you were the first one that came up