Is Grade 8.8 hardware sufficient enough for the suspension hardware that requires high torque values?

I think I read it was... but I need to make sure.

Thanks!

I think I'm using 8.8 for my motor mount, so I hope it is!

if it's big enough. in case of doubt, use at least what the factory did.

this is not the place for a book on fasteners -- Carroll Smith already wrote that book, and it's excellent. but here's some basics as i remember them...

Metric (ISO) fasteners have two-part numbers -- the first is the strength number, which i think (but with not-very-high confidence bounds) is thousands of kg pre sq cm -- but i don't recall if that's in shear or tension. tension i think, which is one reason why Carroll Smith and others think single-shear is a crime against nature... anyway - that's the number before the decimal. as it's a strength number, any material can be "strong enough" if you've got enough of it...

the number after the decimal is the percentage of ultimate strength at which yield (permanent deformation) will occur.

so - an 8,8 will bend at 80% of its ultimate yield strength. a 10,9 -- the other fastener worth considering in the kinds of things we do (although i have seen 12,9) will bend at 90% of its ultimate failure point. these kinds of fasteners are highly heat-treated to achieve their strength.

VERY approximately -- an ISO 10,9 is equivalent to a SAE Grade 8.
there isn't a good SAE approximation of the ISO 8,8 -- but it's approximately equivalent in characteristics to aircraft hardware.

Smith doesn't like SAE Grade 8 in suspension applications, because since its deformation point is so close to its ultimate failure strength, it tends to be brittle. in suspension (and some other applications) you'd prefer that a bolt bend, if it's going to fail, which will at least let you park the car safely, than break.

IMO - it's worth the trouble to find aircraft hardware for the places it can be used - which is usually just substituting 5/16 for 8mm. you won't be finding metric threads in aircraft hardware, and because of its design, keeping a stock of all the appropriate grip lengths is a PITA... it's good stuff tho.

-somewhere- i have the Carroll Smith fasteners book (not unpacked yet...) so i can't give you the tensile strength number for 8,8 - i'd think a web search, probably on the Earl's Supply site, would turn this up. but you find the strength in kg/sq-cm, figure out the area of the fastener in question, and you will have the actual yield number - that number doesn't relate very directly to actual torque numbers needed to produce that tension - which is the subject for yet another chapter in the Fasteners book - relating torque to tensile stress and why for critical applications (e.g. connecting rod bolts...) what you really need to do is measure the actual bolt stretch...

These people have a excellent write up in the catalog of the different ratings of fasteners. They have always been able to supply any metric nuts,bolts,pipe fitting or tubing I needed.



http://www.metricmcc.com/

Yep. We used MM in Dallas for years and years...


B

Hi,
I bought some stainless steel bolts for my motor mounts. The head of the bolt is stamped with A2-70 with THE below. I think it's strong enough?? At least it wasn't cheap. Expensive means strong rite?
Cheers, Elliot