Guide 16 · Fastener Reference Guide
Galling
Why stainless fasteners seize during tightening — and how to stop it.
Text version — searchable and screen-reader friendly
Galling — also called seizing, cold welding or pick-up — happens when two metal surfaces are pressed together hard enough that they bond rather than slide. Stainless steel accounts for the majority of cases.
Stainless owes its corrosion resistance to a self-generating passive layer of chromium oxide, which shields the metal beneath from oxygen and moisture. As a stainless nut runs down a stainless bolt, friction scrapes that layer away. The exposed base metals make direct contact and weld together, and continued tightening strips the thread or twists the fastener off.
How to prevent it
- Slow down — hand-tighten stainless where possible and avoid impact drivers
- Use an anti-seize lubricant on stainless and galvanised threads
- Keep threads clean; grit accelerates galling
- Don't run a nut up and down a long thread repeatedly
- Pair dissimilar grades (for example an A2 nut on an A4 bolt) on problem joints