Are there different grades of metric bolts? I need longer spindle bolts, and I want the right strength bolt.

Yes, there are different grades:

I think Metric Property Class 8.8/9.8 (depending on size) is roughly analogous to SAE Grade 5, and 10.9 is roughly analogous to Grade 8.

There are other intermediate and/or special grades in both systems, and they aren't exactly the same, but those seem to be the common ones (other than stainless and the ordinary low carbon grades).

oh YES THERE IS...ask me how I know....







Grade 8.8 equals "roughly" grade 5 standard.....i.e. NONO!

Grade 10.9 is "roughly" grade 8 standard.....i.e. what most GM suspension bolts are....

As you can see from the pic above, I drilled mine out and replaced with AN bolts with a nut on the back....JonA has drilled his out to 12 mm from 10 mm I believe....

Thank you. The stock one says 10.9 on it, the cheap ones I bought for mock up say 8.8. I was not sure if that was the grade rating or some metric nonsense.

8.8 = baaaaaad!

Wow I type slow. Randy, that looks like hell I almost had the same thing happen when a spindle bolt fell out and locked up the rotor. Good thing I was just going real slow down a dirt road scouting for Quail.

That must be a heavy hopped lager ale if it shattered that rotor ....

If that is the definition of Miller time, I can imagin when things go well. :drive:

Note there is counterfeit hardware out there posing as the real stuff. Try and by a name brand fastener from someone like Holochrome, SPS Unbrako (socket Head).

Here are some sources for known good product:

http://www.atlanticfasteners.com/ (I use these guys) One to two days shipping time to me.

http://www1.mscdirect.com/cgi/nnsrhm

Most sources will require box Qty.

AN Fasteners (Mil Spec) you can use:

http://www.coastfab.com/boltsseries.html (Also a good source for info on Mil fastener info)

Thanks for the links. I ran all over town today looking for the right bolts. I found a place that has about every kind of nut and bolt you can imagine. Had I seen the links I would of just made a phone call instead.

So should I be afraid that home depot (hillman brand) grade 8 bolts hold in my lap belts?

Thing I would be worried about from Home depot is source of said bolts.

Chinese steel = crap

Also, if you can find them, "rolled" threads are much preferred over your normal cut threads. Grade X is just specifying the ultimate strangth of the bolt.

Rolled threads actually strengthen the threaded region where cut threads will make it weaker since you have sharp points at the bottom. All our threads are rolled at work, we have a thread rolling machine. Needless to say when you have almost 300,000 pounds of force reversing on a piston rod 5 or 5.5 times a second and you're compressing hydrogen you don't want cut threads.

Other things to look at is to ensure there is enough stretch on the bolts. Proper torque and lubricant (anti-seize has a lower nut coefficient than mineral oil and we have two seperate torque tables at work that we provide to our clients) are important to get the right pre-stress in the bolt. There are many boltings that have literally no stretch. You should have at least 2.5 times the diameter free length of the bolt to stretch (not engaged in the tapped hole). This is most important on bolting that sees cyclic loading. The idea is to always have the bolt in tension rather to have it cycle between tension & compression.

Tightening a weaker grade bolt to a higher grade bolt torque specification can yield (damage) the bolt.

Randy, did your bolt break at the first thread?

I think so...the bolt was gone so I can't be sure...

You can see in the photo, that all the bolts were BENDING about 1/4 inch down from the head....and the threads were working into the bracket....I think Jon's Brake force that bent his Movit brackets were working HARD on those bolts....

I thought as long as they met specs they would've been ok, guess I'll switch bolts. I am aware of proper preload however and put them on with loctite and used the torque chart for lubed grade 8 fasteners with the same dia and pitch.

Loctite has the same effect as a light oil on torque values correct?

Thanks.

Part of the below statement is from:

http://www.coastfab.com/torque&fastener.html

There is a way to test bolts by exceeding there torque spec. until the bolt reaches its yield point (the point at were bolt will undergo "plastic" deformation (permanent stretch). Bolts for critical applications should be test-torqued to determine the point of measurable permanent stretch. As a rule, approximately 90% of this value will give the best performance in a bolted assemble.

Now if the bolt deforms below spec. it is not what it is purported to be.

Yeah. Despite feeling those brackets could have been stronger, it was pretty sobering to realize I was bending steel brackets. That's a lot of force....

Since we're talking about bolts... I saw a website where a company was advertising a new type of tap. They were saying that their idea was better than average because the threads were cut differently. I can't remember what the exact details were, but the way I was told the bolt wouldn't break at the first thread that enters the tapped section. So that leads me to the question, will the bolt break halfway into the threaded section? They also claimed their system is on the space shuttle. Does anyone have an opinion on this?

Never heard of different kinds of taps. Typicall the bolt breaks rather than the thing it is screwed into. When you think about it the item that is tapped is larger (and stronger) than the bolt.

The majority of bolts do break at the first thread. Cutting threads into bolts adds a stress riser. By rolling threads onto bolts you are maing the bolt stronger by cold-working it AND you are moving the grain structure of the metal. Think of the metal as having layers. When you look at it sideways you are cutting VVVVV across the layers and are weakinging the structure. Rolling threads moves the material and keeps it continues.

As far as I know all internal threads (tapped) are cut.

Internal threads can be cut (using a die) or rolled (using a sophisticated forming machine). Roled threads are far superior to cut threads.

Somehow I found the link. They're saying that the different shape of the thread lends itself to more even torque and thus are self locking. I'm just wondering what everyone who has a true understanding of this stuff thinks about it.

http://www.spiralock.com/

I took a SAE fastener class last year and we got a presentation from Spiralock during the class. The theory makes sense and it is used in some applications, but in the car industry the extra cost of using this thread pattern is prohibitive. Generally, a manufacturing plant doesn't want to worry about sourcing new thread taps and the like, especially not ones that are more expensive than what they currently use that are also working just fine.

Besides just rolling threads there is also a MJ thread designation that basically has a larger radius at the root of the thread. This makes the bolt even stronger and is used for many engine fasteners, especially rod bolts.