Screwed or pressed in, more likely screwed. If you are trying to replace them, heat will be your friend, but by the looks of it, they have already met the gas axe. 2 nuts locked together and cherry red heat should shift them if they have a thread.
Last one broke. Drilled it to letter size M then melted the thin remaining threads away. Cleaned with an old tap.
I heard that they have opened a plant up in Kitimat as well as St Johns to package that new invention... LOL
I'm just really glad that it is you doing that rather than me. That is way way down on my favorite things to do chart probably on page five.
Most anti seize is rated for pretty extreme temps, 1200-1500 degrees or more. I use it to lube the kingpins while dropping axles. However... you don’t really want those studs threading in and out of the manifold, you want them to stay put. I’d use some high heat loc tite.
Also, use brass nuts on the studs when you install the exhaust pipes. If I remember correctly, they are typical Ford studs : coarse threads into the block and fine threads for the nuts.
I'd use the "Never-Seize". I have never heard of bolts or studs falling out because of it's use. Even if it does no good at all (which I do NOT believe), you would be no worse off than if you didn't use it. I love "Never-Seize" (except for the mess it makes if you're not super careful).
I didn’t say they would fall out I said you don’t want them to come out after they’re installed, you want the stud to stay put and the nut to come off. If they were intended to thread in and out of the manifold they would be a bolt not a stud.