Nut & Bolt Grades, What does the 8.8 Mean?

xjwmx

I want to replace the nuts on my upper fork pinch bolts and on the single pinch bolt on the steering stem.

I think these are grade 9 bolts. My question is, is just any nut strong enough to match the bolt? I mean there's no marking on any nuts that I know of...

kyle1911 · Posted: April 25, 2009, 12:13 pm Post subject: Re: Nuts for bolt grade

Unless someone has better info...Virtually all the fastners on these machines should be a SAE Grade 5 metric equivalent. Axles, and some engine fastners may or may not be harder, I don't know. Grade 5 fasteners are a good mix of strength and flexibilty. Grade 8 is a little stronger, but will break, instead of bending. For most applications, grade 5 is the way to go. It isn't lesser, just more ductile, and will give warning before "Snapping" If you want a graphic experiment, put one grade5 bolt, and and equal grade8 in a vice, and bend 'em over with a pipe. The 5 will nearly "U" , the 8 won't make 90 degrees. If it makes you feel better, the much hallowed AN fasteners used in aviation, are grade5, with rolled, not cut threads, that are cad plated, and inspected. As for the nuts, I used standard grade5 Nylock on mine, no worries at all, and I prefer them to lock washers. Hows that for a long answer? Geeze, I ramble. Kyle

yamaman · Posted: April 25, 2009, 12:42 pm Post subject: Re: Nuts for bolt grade

For those interested!
On metric bolts, you often see on the head a number like 8.8.
These numbers indicate the tensile strength of the bolt.
The first 8 means nominal (minimum) tensile ultimate strength, 8 = 800 MPa = 116,030 psi.
The second 8 means nominal (minimum) tensile yield strength 0.8 times tensile ultimate strength, 0.8 x 800 MPa = 640 MPa = 92,824 psi.

A imperial grade 5 bolt (indicated by 3 radial lines on the bolt head) has a tensile strength of 110,000 psi and a proof load of 85,000 psi!

Easy really isn't it!

So we can say roughly that a grade 5 SAE bolt is pretty much equal to a metric 8.8 bolt!

Nuts should be matched to the bolt being used, a 8.8 bolt should have a class 8 nut. Or a grade 5 bolt should have a grade 5 nut!

The link attached shows different identification markings for various nuts and bolts!

www.warburtons.com.au/.../00007.pdf

jayel · Posted: April 25, 2009, 1:57 pm Post subject: Re: Nuts for bolt grade

this bolt info would be a good keeper for "The Vault"

xjwmx · Posted: April 25, 2009, 2:44 pm Post subject: Re: Nuts for bolt grade

Ok, according to the pdf, nuts are marked too, as are washers, and should be selected to match the bolt.

BigGeorge · Full Member Joined: Apr 13, 2008 Posts: 267

Thanks Yamaman, Good Post !!!!!

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

That's good info, yamaman. But is it good in the 'States, too?

yamaman · Posted: April 25, 2009, 8:05 pm Post subject: Re: Nuts for bolt grade

AS/NZ standards are usually equal or above international standards.

The metric stuff is all ISO, so yep should be good the world over! Cool

I'm sure you get the same bolts we do (unless they put special bolts in for you guys Smile

), like the 8.8 type. Of course the imperial info I posted is from the Society of American Engineers (SAE).

You'll all have to check your nuts! Shocked

yamaman · Posted: April 25, 2009, 11:40 pm Post subject: Re: Nuts for bolt grade

650skull wrote:

Good post, In addition to the info there nuts have 2 sides, (a bit obvious). .................The contact face is usually larger on one side of the nut than the other giving it more of a contact surface = more strength

Probably obvious to most, but.....
Just on that, with normal type nuts that are ambidexrous.
When you remove them, you'll notice the in side is clean and slightly polished from wear, and the out side might be a tad grotty. Always best to put them back on the same way you got them off if you can!

Also worth noting, is stainless fasteners, while they look pretty, are generally of a lesser tensile strength than equivilent black steel!

chilliwackwestie · Full Member Joined: Sep 26, 2008 Posts: 37

too much tech !!
you guys are NUTS !
J/K

cheers

jimmythetrucker · Full Member Joined: Mar 12, 2008 Posts: 1283

I used to check my nuts every day. Now I'm older I find it isn't worth the trouble.

nudude53 · Posted: April 26, 2009, 1:21 pm Post subject: Re: Nuts for bolt grade

I just scratch mine as soon as I wake up and I'm good for the day. Can't keep them tight anymore though.

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