NEWS
【NEJIGAMI #Episode 4】Why Penetrating Oil Won’t Free a Galled Bolt
You emptied the can and it still won’t budge — here’s the reason.
"I sprayed a famous penetrant over and over, and the stainless bolt still won't budge." With galling, this is a common story. So why does even a well-reviewed penetrating oil fail? The answer is in **how a penetrant works.**
A typical penetrating oil frees a stuck fastener by **lowering surface tension to creep into the threads, dissolving rust, and lubricating so the parts slide.** On a rusted bolt, this works well. But galling puts up three walls:
**1. There is nothing to dissolve.** Galling is not rust — it is welded metal. A penetrant designed to dissolve rust has no target here.
**2. There is no gap to penetrate.** A galled joint has metal dug into metal with essentially zero clearance. If there is no path in, the oil just sits on the surface.
**3. Lubrication can't break a weld.** All a penetrant can do is make things slide. But no amount of "slide" separates a welded joint. Sliding or dissolving cannot break the physical bond of a cold weld.
The result: on a galled fastener, the oil merely coats the surface. Apply force at that point and the **bolt bends, the shank deforms, or it snaps** before it ever comes loose. In fact, in our own comparison test, **not one galled stainless M12 bolt came out with any of 10 other penetrants — including well-known brands** (full data in Article 6).
The takeaway: galling needs more than "penetrate and lubricate." It needs a mechanism that acts on the **welded metal itself and breaks the bond.**
**Related articles**
- Article 3: [Seized Bolt: Rusted or Galled? How to Tell the Difference](https://neji.jisscrew.com/news/detail.php?id=342)
- Article 5: [How to Remove a Galled / Seized Stainless Bolt Without Cutting or Heat](https://neji.jisscrew.com/news/detail.php?id=340)
**When penetrating oil has already failed**
**[NEJIGAMI]**https://www.jisscrew.com/details/index.php?cid=168 was developed for exactly this — galling that ordinary penetrants can't touch. See its mechanism and the test data in Article 6.
This article is part of our complete guide: Stainless Steel Galling — Causes, Removal & Prevention