Well I found my old exhaust manifold bolts and I checked them with a tap and the threads matched M8x1.25 and when I mic'd the with a pair of calipers, I got 7.91mm. Hope this helps.
yep, that's right. We run a tap down every hole, 8x1.25 is is, for sure.
yep there 8mm 1.25 bacause the torque spec in book matches a 8mm bolt
The only metric stainless studs ARP makes are 8mm x 1.25 so I guess that's it. $154.74 for 16 studs and nuts. WTF is up with that?
Honestly mitch, I wouldn't waste the money. We see a ton of these heads come back with stripped out bolt holes in the exhaust. I don't know if it's people fighting with the manifolds taking them off or putting them on in the truck, and f-ing the threads all up in the process, or if people are over torqueing them, or what, but The 8x1.25 bolts themselves just wont take that much torque.
Are your heads off now? If so, drill and tap them out to a 10x1.5, that'll hold plenty fine, and probably will still work in the steed manifolds without having to drill them out, the pics look like they have a plenty big enough hole for the bolts, I know the stock ones have a huge bolt hole, even if you had to run a 3/8" drill bit down the steed manifold bolt holes you'd be fine. If your heads are on, you could maybe still do it if you can get a drill and tap in there. I'll probably be doing it to mine just because when I have it apart, hopefully a long time from now. Then again, 10mm and 3/8 are so close, you could probably just tap the exh bolt holes in the heads to 3/8 and the arp bolts/studs would probably be way cheaper for standard thread. Don't forget to use anti-seize...also, perhaps stage 8 locking fasteners has something that would work...just thinking outloud. I'd seriously consider moving up a size in bolts though, 8mm is nothing (almost the same as 5/16).
EDIT: there's plenty of meat there in the heads too, you don't have to worry about going into the water jacket if you do it right...drill it and tap it nice and straight, obvously easier said than done in the truck. just don't go much deeper than the stock bolt holes are, I want to say they're about .900" deep or so, I could be wrong on that, I can double check tomorrow.