JIS (Japanese) bolts

[Nenw]

For the sake of appeasing my curiosity, what do the numbers on the bolts all represent? I was thinking hardness but metric bolts are represented with a decimal. I searched out JIS but The internet doesn’t seem to know if JIS has its own hardness system. Maybe i used bing by accident. Probably why all that porn showed up.

Thanks y’all

 

[Nenw]

I did a deeper dive on this and put a sweet little chart together. Following is info from the service manual.

What I've found so far is that the bolt head markings on Mitsubishi Bolts don't correspond to anything in the real world. JIS bolts seems to follow metric bolt hardness but I question that a little bc when does that ever happen?

The max torque spec between Mitsubishi 4 and Metric 4.8, Mitsubishi 7 and Metric 8.8 are almost identical. These are in NM and for dry bolts.
Also, know that the thread pitch between what is specified by Mitsubishi and the other bolt chart don't match 100% but they are close. It is really challenging to find identical bolt spec listed listed.

The reason I dove into this was bc I am constantly replacing bolts on the van. I typically purchase metric 8.8 bolts but wasn't quite sure if that was the right thing to do. I am in the middle of the 2" body lift from Dreamworks and the washers are all made of bubble gum which had me questioning the rest of their bolt choices. I couldn't get a proper torque spec on anything due to bubble gum washers squishing and ripping out during tightening to factory spec. It had me concerned hence this deep dive.

Moral of this story, there is a bolt spec, follow it, don't buy bubble gum hardware or your body and chassis might separate while driving down the road which, while exciting is not not going to be welcome.

 

[Nenw]

To further make the matter confusing for people, metric and sae are on a totally different scale as well. In terms of tensile strength:
SAE Grade 5 = metric 8.8 = mitsubishi 7
SAE grade 8 = Metric 10.9 = mitsubishi 10?

@Growlerbearnz , i agree however when i pulled out the hardware from the subframe all bolts Were marked with a “7” on the bolt. The bolts that shipped with the kit were 8.8 hardness so that would correspond, be it probably by luck. I am wondering if the reason the bolts are not a 10.9 is because those Would likely be so hard that they just might tear things apart in the event of an accident. Rather than bolts bending and being replaceable?

I did notice there were a few bolts on the van with a 10 marking. At the lower front shock mount And another spot that is escaping me at present. Those aren’t even called out in the factory manual. My guess is that those likely reference something closer to a grade 10.9 bolt.

Anyway i wouldn’t take this all as gospel but the initial info is there to help make more sound decisions. Again you should almost always buy hardened very few reasons not to. And if you happen to have access, jis as well. I am fortunate in that my local hardware store carries Jis10.9 bolts. Amazing!

 

[Growlerbearnz]

Additional info:
If you have a missing bolt and you're not sure what it should be, one way to figure it out is to head to the parts catalog and look up that bolt, like so:
View attachment 11433

In the description it says "10x25" so that's M10(1.25) x 25mm long. (Mitsubishi M10 bolts are mostly a 1.25 thread pitch).

To find the tensile strength, throw the part number (MF241282 in this case) into Google images and find an image that shows the bolt head:
View attachment 11434

That bolt has a "7" on it, so as per the awesome chart from @Nenw above, you want a metric class 8.8

...one caveat though. Mitsubishi (and most other Japanese car) M8 bolts have a 12mm head, most hardware store M8 bolts will have a 13mm head. They'll fit, but you'll need one more size of wrench to remove that part, which gets old real fast.