Slick 60's

I'm replacing one of the exhaust donuts on my 352 and removed the studs from the manifold to the exhaust pipe/flange. They seem to be of the 7/16 variety but the 7/16-14 and the 7/16-20 bolts at the parts store seemed to be not quite right.
I did some googling and forum searching but couldn't find an answer. Does anyone know what the thread size is for these studs from factory?

7/16 is right , but there is an oddity to those studs. The threads are not cut like regular bolts. Try running a die on one and you will see what I mean. If I remember right, the threads are not cut as deep on the studs. Not certain why Ford did this, but wonder if it has something to do with nuts seizing on the studs, and or seizing in the manifolds. Be sure to use antisieze on anything yo put back into the manifold. I usually re-tap the holes then just install regular studs. You might ask at your local parts house if the original style studs are available, or try your Ford dealer. More than likely, the dealer can't even look up the part numbers but you never know. Original nuts may have been brass. There were two kinds of donut rings for our trucks , one was graphite impregnated and the other a steel ring in case you did not know.
Rich

Thanks for the response Rich. For now I think I can get away using the old nuts/studs with antiseize. Sounds like the most convenient thing to do is tap the holes for regular studs.

The donut I got is the metallic kind. Is there an advantage of using one over the other?

oddly i have never given this any thought.i have replaced countless studs, they always seemed to thread into the manifolds so the tapped holes in the manifold must be the normal 75% thread and the factory studs made to tightly thread in the holes maybe an extra 5%
im guessing the nuts are normal like the manifold threads so they are tight fit as well

regardless the replacement studs from the store do fit and new brass nuts will work on old factory studs i know cause i have them on my y block


http://www.lincolnmachine.com/tap_drill_chart.html

Thanks Ice, that's good to know