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【NEJIGAMI #Episode 3】Seized Bolt: Rusted or Galled? How to Tell the Difference
Mistake the cause, and your very first move is wrong.
"The bolt won't come out" can mean two very different things. Confuse them, and you will choose the wrong fix from the start.
**Cause 1: Rust and corrosion.** A steel bolt corrodes outdoors or in wet conditions, and iron oxide expands and packs into the threads. This is the classic **rusted bolt.** Most off-the-shelf penetrants (rust penetrants) are designed exactly for this — dissolve the rust, creep into the gap, and lubricate so the fastener slides free.
**Cause 2: Galling (cold welding).** As covered earlier, this is not rust but **metal cold-welded to metal.** It is common in stainless, aluminum, and titanium. There is **no rust to dissolve here** — only a solid weld where two pieces of metal have fused.
The symptom ("it won't turn") looks the same, but the physics are completely different. **Rust is loosened chemically, by dissolving it. Galling is only freed by cutting through the welded metal itself.** That is the decisive difference.
So using a rust-oriented penetrant on a galled stainless bolt will not do what you expect. There is nothing to dissolve, and lubrication alone cannot break a weld. Force it, and the bolt bends or breaks before it comes loose — something our own comparison test confirmed repeatedly (Article 6).
**First, identify which one you have.** An outdoor steel bolt is likely rust; a stainless-on-stainless joint that suddenly stopped during assembly is likely galling. Different causes call for different chemistry.
**Related articles**
- Article 1: [What Is Galling? Why a Stainless Bolt Seizes and Won’t Come Out](https://neji.jisscrew.com/news/detail.php?id=344)
- Article 4: [Why Penetrating Oil Won’t Free a Galled Bolt](https://neji.jisscrew.com/news/detail.php?id=341)
**If it's galling, not rust**
**[NEJIGAMI]**https://www.jisscrew.com/details/index.php?cid=168 is built to cut through the welded metal of a galled joint, not just dissolve rust.
This article is part of our complete guide: Stainless Steel Galling — Causes, Removal & Prevention