SAE Grade-8 bolt snapped @ 135ft/lbs

How do you know they are grade eight? Have you tested them? There are a lot of counterfeit bolts out there.

Counterfeit bolts??? I was under the impression that if they are labeled as "grade-8" and have the 6 markings, they're grade 8.

Well, first, 135 ft-lbs corresponds to a stress of about 100,000 psi, about 80% of the nominal 130,000 psi rated yield stress. This assumes fine thread (coarse is much worse), and to me this seems a small safety margin. Second, this also assumes a typical lubricant like oil on the threads - are you putting them together dry, or oiling them, or using some kind of anti-seize? Clean and dry gives the most friction and the least clamping force, and the least reproducible clamping force. Third, if you want a more uniform clamping force for a given torque, you should torque, loosen, torque, loosen, and then torque to final value to burnish the threads and underside of the head (or 5 cycles if you are paranoid about your head bolts :-)). Sounds to me like you are overtightening your fasteners. Go to

for some good reading.

-- Regards, Carl Ijames carl.ijames at verizon.net

Yes, they can be counterfeit.

Do a google search:

If I were you since it is class 1 safety (potential fatality if a failure) then I would only buy certified grade 8 bolts. I would test some of the ones you have for strength at an independent test lab. Perhaps do a hardness test on a sample of them.

Grade 8 1/2-13 bolts, torqued dry, should be torqued to 110 pounds. Lubricated, to 80 pounds. You know what they say about ASS-U-ME .. :-) GWE

Unbreako!

Uhmm...you probly should consider getting certifications on all of your fasteners then..

I'm thinking the Chinese like to put a few extra little marks on the heads of their bolts...they seem to sell a little faster that way...

Whatever it is your building, appreciate if you dont fly it anywhere near I'm at.

For Grade 8, assuming a minimum tensile strength of 150,000 psi, a 60% load would be 106 ft. lbs. for 1/2-13 or 119 ft. lbs. for 1/2-20.

Assuming "ultralight" means you are working on an ultralight..... AC43.13-1B gives 73 ft. lbs. and 91ft. lbs.respectively for AN310 (90,000 psi) bolts.

You are either over-torquing or under-engineering!

Actually, it's not for an aircraft. I'm converting a truck to a solid front axle suspension, and the bolts are holging leaf-spring hangers to the frame......Thank you all for the information!

You want the holes REAMED to make the bolts a light press fit into the frame. You also need to de-burr ALL holes and make sure everything fits together perfectly so the spring hangers can not try to move on the bolts. A grade 8 bolt will not flex very often before it cracks.

Might also want to consider L9 bolts.

Big truck or little? If a big truck, there ought to be a little tag in the center front of the axle describing who made it and what model it is. Call 'em and ask about your application and they will be a whole lot of help and that phone call can save your ass if there's ever an accident. Since you're "converting to a solid axle" I figure it's not too likely you're working on a big truck, but it's worth noting.

Several years ago, all M1 Abrahms tanks had to be inspected for counterfeit bolts used in the main gun mount. Wanna guess how they knew there was a problem?

By the way, I have military surplus aircraft grade 1/4" 1" long square neck carriage bolts. 500,000 PSI. I can sell them in bags of 100 in each.

i

A while back I bought some 'Grade 8' bolts at the local hardware store (I'll use it's name) Orchard Supply and Hardware now a wholly owned subsidiary of Sears. I was honking down on them but no where NEAR a 100 Ft/# Stripped the damn bolt clean as a rod (nut was OK)... I took em back got hemmed and hawed about "Gee we had a few bad bolts in that lot want some replacements for free".. My answer.. NO... Moral... Buy your Grade 8's from a reputable supplier and if it's at all critical ask for paper that's 'Nine Nines and traceable to the mine"...

Dave

Those must be damn good bolts. I know ARP have got bolts that run close to

300,000 psi and that's pretty much state of the art so 500k psi must be alien technology I reckon. Maybe bolts pinched from flying saucers at Groom Lake, if flying saucers actually use bolts that is.

Want to give us a material spec on those first? Unobtanium alloy perhaps ?

On Wed, 09 Mar 2005 02:30:39 GMT, "Carl Ijames" vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

Sorry. I am following this with interest, not judgement. But wouldn't coarse pitch place _less_ stress at a given torque? For a given torque on the head, surely you are pulling much harder on the steel with a fine thread.

You can use them on the bridge I'll sell you ;)

Haha, thanks for pointing it out. It turns out that they are 55,000 PSI per square inch. Sorry for the confusion.

i

Sorry, my recollection was wrong, they are 55,000 PSI.

i