Stud M12 X 1.5 X 46.6 (6 Each required) Isuzu/Honda part # 8-97115-132-0
The 1.5mm thread is for the manifold side because the nut side is 1.25mm

Nut , Stud
12mm X 1.25mm (6 Each required) Isuzu/Honda part # 8-97170-524-1

 

Stud M12 X 1.5 X 46.6 (6 Each required) Isuzu/Honda part # 8-97115-132-0
The 1.5mm thread is for the manifold side because the nut side is 1.25mm

Nut , Stud
12mm X 1.25mm (6 Each required) Isuzu/Honda part # 8-97170-524-1

Why would the nut be different than the stud? Thanks for the info but I don't understand that. I have a thread chaser for a 12mm 1.5 and 1.75 but not a 1.25. Replacing the stud is not an option, I can't get it out. Any suggestions??

 

The stud has two different threads and a torx (smaller than the stud) to screw it into the cast iron manifold (once install, they usually rust/weld themselves in permanently). The treads that go into the cast iron are 1.5mm and the exposed stud has 1.25mm threads for the nuts that tighten the downpipe flange.

 

Most fine thread nuts and bolts on Isuzu trucks are 1.25mm. The exhaust stud has two different thread pitches 1.5 on the manifold side and 1.25 on the pipe side.

 

Most fine thread nuts and bolts on Isuzu trucks are 1.25mm. The exhaust stud has two different thread pitches 1.5 on the manifold side and 1.25 on the pipe side.

Ok I see what you are saying now. I need the pipe side which is the nut side, Well just wasted 22 bucks on a thread chaser set that doesn't have what I need. Thanks again.

 

Thank you to B28 for those part numbers. I'm in a similar situation and weighing options. I've got 3/6 good studs and no nuts. Going to Honda Parts or Isuzu is running $60+. Ouch. Are there any other less expensive sources? I hate to say it but I'm also debating removing all studs, drill, helicoil, and going with inch GR8 hardware. ??? Any thoughts?
A simpler option I've thought of is just using an M12-1.5x40 bolt. Advance Auto Parts has those. 6 would be$25. I could probably get them even cheaper at a bolt supply company. I guess that opens the stud v bolt debate.

 

Thank you to B28 for those part numbers. I'm in a similar situation and weighing options. I've got 3/6 good studs and no nuts. Going to Honda Parts or Isuzu is running $60+. Ouch. Are there any other less expensive sources? I hate to say it but I'm also debating removing all studs, drill, helicoil, and going with inch GR8 hardware. ??? Any thoughts?
A simpler option I've thought of is just using an M12-1.5x40 bolt. Advance Auto Parts has those. 6 would be$25. I could probably get them even cheaper at a bolt supply company. I guess that opens the stud v bolt debate.

These nuts are less expensive:
https://www.amazon.com/Liberty%EF%BC%8C ... 558&sr=8-3

 

Hey B28. Are you sure about those threads? I just pulled the studs out of the manifold (flange joint). The threads in the manifold appear to be M12-1.25. I ran a thread restoring tap into them. 1.5 was binding up but the 1.25 was smooth. Could the studs be M12-1.25 manifold side and M12-1.5 nut side?

 

Could the studs be M12-1.25 manifold side and M12-1.5 nut side?

I don't have a stud available to check the thread pitch, what is the pitch on the nuts you removed?

 

Hmm. Well, I don't know. I obtained this engine with manifolds intact. But the nuts were gone. One stud was missing, two had damaged threads. I just decided maybe it would be best to remove them all. So I did. A tad southern, but I welded a 1/2" nut onto the ends. I started using the impact, which worked good on one, but found that it would just shear the bolt off on the others. I recruited PB Blaster for a long soak and removed the remaining with a ratchet and cheater pipe.

So, yada yada yada, I don't know if they are M12-1.25 or -1.50 on the nut side. I held them up to my thread tool for sort of a profile comparison but that was just a guess.
I suppose I could take a stud over to the bandsaw, cut the weld nut off, bevel the edge, and try to run a nut on it and see, but at this point I think it's just moot. It's going to be replaced and I can drive what thread to use.
What's the kicker is that I don't have scads of metric hardware laying around, especially in the flavor variety of coarse, fine, and very fine. I'm still debating just converting to bolts and calling it done.

 

For $16 you can find out: https://www.amazon.com/INCH-METRIC-GAUG ... h+&sr=8-10

Or even cheaper, couldn't you just drive to the hardware store and use theirs?

 

Yes. Good tip Enemigo. I might break down and get one of those.
I went ahead and sourced M12-1.25 x 35mm bolts from Bolt Depot. I ran a thread repair tool through all holes. The outer two holes, on each side, were tapped through. It was only the inner hole, again on each side, that was only partially tapped. That said, the ideal bolt length would have been a 30mm.
I could trim the inner bolt down but it's not that big a deal. They're all going to get a washer and a lock washer as well.
Here is my new exhaust staged.