Thread: M12 grade 8.8 "high tensile" bolts

I don't know if it was always this way or not but most bolt suppliers I go to, if I say "high tensile," I'll get 8.8. If I want 12.9, I have to specifically ask for it and hope that they actually have some.

I tend to favour Unbrakos because at least you know what you're going to get.

class 4.6-240mpa yield, 400mpa tensile

class 8.8-640mpa yeild, 830mpa tensile

class 12.6-1100mpa yield, 1220 tensile

Around these here parts, for going on 30 years, 8.8, 10.9 and 12.9 have been known as high tensile according to the boxes. Thinking of shcs perhaps?

You have got to wonder about some of the Indian stuff, I've seen a beyond 12.9 spec on something or other a while ago, must be equivalent to chalk!

I would agree with the others here Bob, grade 5 imperial or 8.8 metric and above was high tensile, mild steel was not. Also agree with Diomedes that Unbrako and also Cat bolts are the real deal.

Originally Posted by bob ward

Came across this recently.

Last I knew a metric grade 8.8 bolt (imperial grade 5) wasn't considered to be high tensile, that was the province of imperial grade 8 or metric grade 12.9 bolts.

Bremick have been in the bolt game for many years so I guess they know their stuff. Is the accepted definition of "high tensile bolt" weakening, or is Bremick stretching the truth here?

I thought that any bolt of grade 8.8 or higher would fall into the category "high tensile bolt". Some people also call grade 8.8 "structural grade", probably because bolts of less than grade 8.8 are often not even stamped with a grade.

However, there is no clear and recognized definition of what a "high tensile bolt" actually is meant to be. That is why Engineers prefer to talk about a specific grade rather than just "of high tensile". Take note that in recent years there are masses of "fake" grade bolts around, usually from obscure Chinese origin, stamped 8.8 alright - but in reality so soft they stretch far more than a 4.6 ever would.

Just for comparison: unlike "high tensile bolt", the expression "Aerospace bolt" does have a precise meaning even without mentioning the grade. It means that the bolt is certified, manufactured from standardized stock material and using a traceable process. The whole history of the bolt must be recorded, and if the bolt fails, its manufacturer may be liable for the consequences.

Originally Posted by cba_melbourne

I thought that any bolt of grade 8.8 or higher would fall into the category "high tensile bolt". Some people also call grade 8.8 "structural grade", probably because bolts of less than grade 8.8 are often not even stamped with a grade.

However, there is no clear and recognized definition of what a "high tensile bolt" actually is meant to be. That is why Engineers prefer to talk about a specific grade rather than just "of high tensile". Take note that in recent years there are masses of "fake" grade bolts around, usually from obscure Chinese origin, stamped 8.8 alright - but in reality so soft they stretch far more than a 4.6 ever would.

Just for comparison: unlike "high tensile bolt", the expression "Aerospace bolt" does have a precise meaning even without mentioning the grade. It means that the bolt is certified, manufactured from standardized stock material and using a traceable process. The whole history of the bolt must be recorded, and if the bolt fails, its manufacturer may be liable for the consequences.

Regarding the "Aerospace bolt" I was watching the Air Crash Disaster show on tv not that long ago, and yes, having the wrong grade bolt in a plane is a bad thing. There were multiple cases of dodgy parts suppliers selling fake bolts to major airlines et.c with catastrophic results. The price differences were amazing - a 1000% in some cases. Sellers and buyers were actually sent to jail in the US over it.

Getting back on track, I always thought Grade 8.8 bolts were high tensile.

Ben

Originally Posted by bwal74

I always thought Grade 8.8 bolts were high tensile.

Ben

Me too.

It looks like I'm the only one in step here.

Thanks for setting me straight.