Seizure is not rust. It is metal transferring onto metal under pressure until the two surfaces are effectively welded at a microscopic scale, and the thread can no longer slide. Stainless fasteners are particularly prone to it because their oxide layer regenerates instantly and welds to itself under load.
This is why a stainless nut can feel fine on assembly and be immovable a season later, even on a part that never saw salt. The mechanism is contact pressure plus movement, not exposure.
The worst combinations are the ones that look most sensible: a stainless bolt in a stainless nut, or a stainless fastener into a stainless flange. Identical alloys share the same crystal structure, so there is nothing to stop the surfaces bonding once the oxide is disrupted.
That is what happens on welded stainless assemblies, where the fastener and the part come from the same family of material. A TIG stainless steel welded part fitted with matching hardware is a joint that will fight you next time unless something is put between the surfaces.
Heat accelerates the process in two ways. It grows the oxide layer, which is the material that bonds, and it changes clearances as the parts expand at slightly different rates. Repeated cycles work the joint and break the oxide again and again, exposing fresh metal each time.
Exhaust flange hardware lives in exactly this condition, which is why it seizes more reliably than hardware elsewhere on the car. Fasteners that stay cool and undisturbed rarely seize, however long they stay in place.
A barrier has to survive the temperature and stay in place during assembly. Anti-seize compounds with a metallic content are the usual answer on exhaust hardware, because the metal carries the load and prevents direct metal-to-metal contact. Grease alone burns away and leaves nothing behind.
Thread tape is for sealing, not for preventing seizure, and it changes the friction the fastener was designed around. On hot joints it also degrades into a sticky residue that makes the next removal worse. Use the right barrier for the joint rather than whatever is on the shelf.
Apply to the thread and under the head, which are the two surfaces that carry friction. Keep it off the taper of a ball joint, off any surface that has to grip, and off the first thread so it does not contaminate the joint it is meant to protect.
Do not use a barrier where the fastener relies on friction to stay put, or where a locking feature is built into the thread. On exhaust fasteners and fittings the rule is simple: coat what has to slide later, leave alone what has to grip now.
Assume every fastener that has been hot will be difficult, and prepare it at assembly rather than at removal. Barrier on the thread, correct clamp load and no galling at the start all decide whether the joint opens cleanly when the car is older.
If a fastener is already seized, the barrier has failed and no amount of spray will put it back. That is a removal problem rather than a prevention problem, and the two should not be confused when the job is planned.
