Any idea what 'class 10.9' means in a black metric 8x125mm two-inch bolt?

[Bob Stevens]

I needed an 8x1.25mm bolt for removing stuck brake drums. I asked the hardware store for the strongest bolts they had. They had a grade 8.8 (zinc) in SAE sizes but class 10.9 (black) in metric sizes.

The guy was helpful and apologized that the class 10.9 was the hardest he had in metric, and he was sure it was weaker than grade 8.8 - but he wasn't sure 'what' it really meant.

The metric bolt, at $1.25 each, has a 10.9 stamped on the hex head.

Any idea what 'class 10.9' means in a black metric 8x125mm two-inch bolt?

[dpb]

On 9/17/2012 6:22 PM, Bob Stevens wrote: ...

Well, he's wrong...it's 'tother way 'round.

Same as SAE Class 8. 8.8 is Class 5

I don't know what the numbers represent other than they correlate w/ SAE grades. I'll leave that as "exercise for the student"... :)

[Ed Pawlowski]

It is stronger than 8.8. You can see the specs here

It is one of the strongest bolts available for tensile strength.

[Bob Stevens]

That's good it's strong on tensile strength because I want to use it to remove brake drums.

Based on the charts, it seems that the word "Class" is merely the metric (i.e., ISO) set of standards while the SAE uses "Grade" and the ASTM uses "Type" and "Grade" - but it seems they all connotate the same thing.

[Bob Stevens]

Here is a picture of the two "ISO Class 10.9" bolts I bought:

Is there any special reason for them being black?

[Erik]

In this nick of the woods (So Cal), brake drum's usually come off without much trouble. I have a couple of garden variety, unknown grade M8 X 1.25 bolts in my box dedicated to drum rotor pulling that now have

35 plus years of use on them. Never recall needing to use more than 5 ft/lbs or so.

Then again, I don't do a 'lot' of brakes, but even so, I bet they've seen use over 100 times through the years, and still look new.

YMMV if you live/work in rust country.

Erik

[dpb]

On 9/17/2012 9:50 PM, Bob Stevens wrote: ...

Black oxide corrosion coating...

As for reason, I guess it's 'cuz they're what was in the bin. :)

--

[DerbyDad03]

I'm not sure if this is correct, but it could just so you know what grade they are.

Most grade 8 bolts and washers I've purchased are gold-ish in color, but it's just a coating. For example, if you extend the threads of a grade 8 bolt up onto the neck, you'll exposed the silver below the gold-ish coating.

Could the colors just be "coding" so you know what grade you are using by sight?

[Smitty Two]

The black is probably black oxide, as someone else mentioned. The gold-ish is yellow zinc plating. Zinc is a hell of lot better than black oxide for corrosion protection, but people like the look of the black for some applications.

Someone else linked to a table of head-stampings for different grades. So, the color is a coating, not a coding.

[Tegger]

Bob Stevens wrote in news:k38mah$eg5$ [e-mail]:

In this appication you will be /compressing/ the bolt, not tensioning it.

In any case, the holes in the drum will split /long/ before the bolt ever gets damaged.

10.9 is overkill for brake-drum removal. You can get away with the cheapest bolts from any big box store. If they fit the threads in the drum, they are good to use.

Two things to bear in mind:

1) possible rust ridge behind the shoes, and 2) the center hole rusted to the hub. Do NOT simply keep screwing down on the bolts to overcome either of those situations.

[Bob Stevens]

Got it!

[Bob Stevens]

I didn't even THINK of that!

There is a ton of rust on that hub.

I should have cleaned it off first, and then lubricated it.

Thanks for the idea!

[Tegger]

Bob Stevens wrote in news:k3ajbq$4q0$2 @speranza.aioe.org:

You need to shock it with impacts. An 8oz ball-peen hammer tapped repeatedly around the lugs should do it. You want to tap as hard as if you were knocking loudly on a door. You need many, many impacts to break up the rust. Do this BEFORE applying any penetrant.

Do not neglect the rust-ridge at the open end of the drum! If present, this will require you to back the shoes off using the access hole usually found at the rear of the drums.