They all go into water jacket on a big block. I have broken enough old ones that I like to replace them all before starting. Soak in PB Blaster or similar for a while and you'll have a better chance of getting them out without breaking.
I did know these led to water jackets. I do plan to run headers is it best to run header bolts or some type of stud? I can see the benefit of studs if you have to remove the headers you wouldnt have coolant running like you would with bolts?