Stainless Steel Galling: Why Bolts Seize and How to Prevent It

You are running a nut down a stainless steel bolt, it starts to feel tight halfway, and then it stops dead. Back it off and it won't move either way. Push harder and the bolt twists off. That is galling, sometimes called thread seizing or cold welding, and it is the most common installation problem with stainless steel fasteners.

The good news is that it is almost entirely preventable.

What is galling?

Stainless steel resists corrosion because of a thin chromium oxide film on its surface. When two stainless threads slide against each other under pressure, that film can be wiped away at the high spots. The bare metal surfaces then bond to each other, tear, and pile up, which increases friction and heat, which strips more oxide. Within a fraction of a turn the threads can lock together permanently.

Galling is a form of adhesive wear. It is not unique to stainless steel; aluminum and titanium do it too. Austenitic stainless grades like 18-8 (304) and 316 are especially prone because they are relatively soft, ductile, and work-harden as they deform.

What are the warning signs?

• The nut turns freely, then resistance rises sharply well before it reaches the surface.
• You feel a gritty or squeaking drag instead of a smooth spin.
• The fastener gets noticeably warm, especially with a power driver.
• Once seized, the nut will not turn in either direction, and more force usually twists the bolt off.

If you feel resistance climbing before the nut seats, stop. Back it off a little, check the threads, and lubricate before you continue. Once fully galled, a nut and bolt usually cannot be saved.

What causes stainless steel bolts to gall?

Several factors raise the risk, and they stack:

• Speed and heat. Impact drivers and high-speed drills generate friction heat faster than it can dissipate.
• High load. Galling happens under pressure. Long run-downs under load and high tightening torque both raise it.
• Same material on both parts. A stainless bolt in a stainless nut of the same grade and hardness is the classic case.
• Fine threads. Fine threads have less clearance and more contact per inch. Coarse threads are more forgiving (see coarse vs. fine thread).
• Damaged or dirty threads. Burrs, dents, grit and paint concentrate the pressure on small spots.
• Misalignment. A nut started at an angle, or a bolt through a misaligned hole, loads one side of the thread.
• Prevailing-torque nuts. Nylon insert lock nuts and all-metal lock nuts add friction for their whole travel, so lubrication matters even more.

How do you prevent galling?

1. Use an anti-seize lubricant on the threads. This is the single most effective step. For stainless steel, choose a nickel-based or a metal-free (for example, moly or graphite based) anti-seize. Copper-based compounds are better avoided on stainless in wet or marine service. A thin coat on the male thread is enough.
2. Slow down. Run nuts down by hand or at low speed. Avoid impact drivers for final tightening on stainless.
3. Don't over-tighten, and adjust torque for lubrication. A lubricated thread turns more of the applied torque into clamp force. If you follow a torque spec written for dry threads, reduce it for lubricated ones (the lubricant maker usually lists a correction) or you risk stretching the bolt.
4. Prefer coarse threads. For general stainless assemblies, coarse thread (UNC or standard metric coarse) galls less readily than fine.
5. Keep threads clean and undamaged. Wipe off grit, keep fasteners in their packaging until use, and don't use a bolt with visibly nicked threads.
6. Start nuts straight. Spin them on by hand for the first few turns to confirm they are not cross-threaded.
7. Consider different materials for the nut and bolt. A harder nut on a softer bolt, or a dissimilar alloy, is less likely to cold weld than two identical parts. In corrosive environments, check galvanic compatibility before mixing metals.

Do washers help?

Washers don't stop the threads from galling, but a smooth flat washer under the turning nut reduces friction at the bearing face. Less friction there means less torque is needed to reach the same clamp force, so the threads see less stress during tightening.

How do you remove a galled nut and bolt?

Once galled, the threads are welded together, so the realistic options are destructive:

• Nut splitter. Cuts the nut away without damaging the surrounding part.
• Cut the bolt. A reciprocating saw, oscillating tool or angle grinder through the shank.
• Drill out a small bolt that has twisted off in a tapped hole, then re-tap or use a thread repair insert.

Penetrating oil and heat rarely free a truly galled stainless joint the way they free a rusted one, because the problem is metal bonding, not corrosion. Replace both the nut and the bolt afterwards; never reuse galled threads.

The bottom line

Stainless steel fasteners are an excellent choice for corrosion resistance, but they need a little more care during installation than plated steel. Lubricate the threads, run them down slowly, and don't over-torque, and galling becomes rare. When you're ready to buy, browse our stainless hex head bolts and hex nuts, and check that the threads match with our guide to matching nuts and bolts.