Many engineers have had a stainless bolt nut seize halfway—keep forcing and the shank snaps or threads strip. This is stainless "galling." Understanding the mechanism and preventing it reduces assembly loss.
Stainless (especially 304/316) has a dense chromium oxide film, but under high-speed friction and pressure the film breaks, metal-to-metal contact occurs, and cold welding sticks the threads tighter until seizure. Unlike rust, this is adhesive wear. It is more likely above M10, on long threads and with high-speed tightening.
Stainless self-locking nuts, fully threaded bolts and unlubricated pairs gall more often.
First, slow the driving speed—manual or low-speed power tools cut frictional heat. Second, use anti-seize compound on stainless threads (copper, nickel or solid-lubricant types), not ordinary oil. Third, pair dissimilar materials, e.g. stainless bolt with zinc nut, or different grades, to reduce like-on-like contact. Fourth, choose plated/passivated surfaces and avoid rough threads.
Fifth, control torque and don't over-tighten. Sixth, clean threads of burrs and debris before assembly.
Once seized, don't keep forcing. Penetrating lubricant and waiting, then try reversing; gently heat the nut (with fire/temperature limits) to expand it. If that fails, cut the nut or drill the bolt while protecting the joint.
High-temperature exhaust and steam joints should use A4-80 or duplex bolts with anti-seize. Trial-assemble critical joints before production. Specify consistent thread surface quality when purchasing.
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