I have no idea where the nuts are that mount the Y-pipe to the exhaust manifold studs. Probably long gone. Are they a special type, or just a standard type of nut?...

 

You could use grade 8 or even better stainless with anti-seize.

 

Brass is also good, used to be considered the gold standard...

New studs & nuts hanging on cards in the Help! (Dorman) section.

 

Manifold nuts are metric 10mmx1.5

'83's might still be 3/8th uss but a lot of nuts and bolts went metric after '82

 

Thanks. I didn't know they were a metric thread...

 

Not sure about that. Seems to me on my 83 they were still 3/8" std thread. Same on both ends of the studs.

 

I'll check...

 

The high flow HO TPI manifolds I just recently sold were metric - M10 x 1.5 like Dyno Don said.
I included new stainless nuts for the buyer to prevent anyone from screwing up the studs with nuts of the wrong thread.

 

These are 1984 H.O. manifolds. Would they have used different thread size on later models?...

 

I don't know if anyone knows exactly when they changed over, and it could have been done mid-production.
But the thread is either going to be 3/8-16 or M10x1.5.

 

Yup, could eeeeeezily have been one of those year-model type things. No need to get overly **** about it at this point.

Worth checking to see what yours is.

Regardless, I think both kinds are hanging on cards right down the street from you. Hell, buy both, put in whatever works, and take the other back for your $3 refund, if you really care enough to waste the gas driving all the way back. If you're a regular customer and 99% of the stuff you buy works fine and they don't have any trouble with you but rather make money off of you and know that when you walk in the store you're a straight-up and honest kind of guy (or girl as the case may be), then they won't mind that in this ONE instance, you encountered an uncertainty.

 

Okay guys, I just tried a 3/8" standard coarse thread nut that I had out in tne garage. That is definitely not it, so it must be the M10x1.5. I appreciate all the replies. Maybe someone can help me on my recent C100 thread as well...

 

Picked up some M10×1.5 nuts today and it's confirmed; that's the size for the stock studs on the '84 L-69 exhaust manifolds...