Had to replace EGR exhaust pipe - trying to bolt it back up to the psngr side header. 3/8ths thread is too big (woin't slide through the EGR pipe at all...the portiont hat is not threaded). 5/16hts thread is way to small and slides in and out with no resistance...10mm thread is also too big. I lost the original bolt.

 

The parts book does not show a size. Maybe 8mm?

 

8mm is too small...i checked it as well(along with the 5/16ths bolts). Strange thing is the GM dealer didn't know either. I'm tempted to just run a 5/16ths bolt through and put a nut on the other end and call it good. That's not gunna be a very good seal though.

 

When I did a set of JBA headers, I had to "chase" the ceramic coating out of the hole for the EGR bolt on #8 tube, and I used a 5/16 - 18 tap. Now that was on the headers, but I would think they would duplicate the manifold setup. I know I didn't buy a new bolt.

If yours is possibly stripped, you would have to drill out the flange hole on the EGR tube to 3/8", and use a self tapping 3/8" bolt into the manifold.

 

I probably should have specified, i titled the thread exhaust manifold beucase that's where the bolt acutally bolts up normally..i have hooker shorty headers though. I just e-mailed holley and am asking them what the thread size is. I wish i would have waited to put the exhaust collector pipe and the starter on until i had the EGR tube bolted up...reaching back there with my huge hands now that the car is completely back to together is a nightmare.