Understanding Thread Galling: Causes, Prevention, and Fastener Choices

What Is Thread Galling?

Thread galling occurs when pressure and friction cause the threads of a bolt and nut to lock together and seize. This typically happens during high-speed installation or when tightening with too much torque.

At a microscopic level, when two metal surfaces—especially softer metals like stainless steel—rub against each other under pressure, their surface oxides can break down. As a result, the metal surfaces start to fuse together. This leads to tearing, welding, and in many cases, complete seizure of the fastener.

Common Causes of Thread Galling

Several factors contribute to thread galling, including:

• Material choice
  Stainless steel, aluminum, and titanium are more prone to galling due to their softer, adhesive-prone surfaces.

• High installation speed
  Fast threading increases heat and friction, both of which make galling more likely.

• Lack of lubrication
  Dry threads create more resistance, accelerating metal-to-metal contact and fusion.

• Over-torquing
  Applying too much torque too quickly can stress threads beyond their tolerance.

• Poor thread quality
  Rough or damaged threads—especially on reused fasteners—are more likely to bind.

How to Prevent Thread Galling

The good news is that thread galling can be prevented with a few simple practices:

1. Use Anti-Seize Lubricants

A dab of nickel- or moly-based anti-seize compound reduces friction and heat buildup, helping the threads glide smoothly without sticking.

2. Slow Down Installation Speed

Avoid using high-speed impact tools on stainless steel fasteners. Slower, more controlled tightening reduces friction and heat.

3. Avoid Reusing Fasteners

Threads may become worn or damaged after the first use. For critical joints, always use new hardware.

4. Choose Compatible Materials

When working with stainless steel, pairing it with a different grade of stainless (e.g., 304 bolt with a 316 nut) can help reduce surface bonding.

5. Use Coated or Treated Fasteners

Zinc-plated or PTFE-coated fasteners provide a barrier between metal surfaces, greatly reducing the risk of galling.

Best Fastener Choices to Minimize Galling

Not all fasteners are created equal. Here are some options worth considering when galling is a concern:

• PTFE-coated nuts and bolts
  These reduce surface friction significantly.

• Nylock nuts (nylon insert lock nuts)
  The nylon insert can act as a barrier to reduce full thread engagement pressure.

• Hardened fasteners with smoother threads
  These tend to gall less than softer or poorly machined ones.

• Bimetal combinations
  Pairing different metals can lower adhesion risk.

• Thread rolling over thread cutting
  Rolled threads are smoother and less prone to frictional welding.

Real-World Applications Affected by Galling

Thread galling is especially problematic in:

• Solar panel frames
  Often assembled with stainless hardware for corrosion resistance.

• Marine structures
  Where stainless steel is preferred but galling risk is high due to exposure and torque settings.

• Aerospace & energy
  Where material compatibility and structural reliability are critical.

In these industries, failure during assembly can lead to project delays, cost overruns, or compromised safety. That's why proper planning and product selection matter from the start.

About Fasto

At Fasto, we understand the real-world challenges that galling can cause—because our customers face them every day. With over 20 years in the fastener industry, we’ve built a global reputation for delivering durable, reliable, and customized fasteners suited to even the most difficult applications.

Whether you're outfitting solar frameworks, assembling marine hardware, or working on precision machinery, Fasto offers a range of anti-galling fastener solutions, including PTFE-coated bolts, bimetal combinations, and custom-thread options.

We also support custom requests for specific materials, coatings, or bulk configurations—so even if you don’t see the exact product on our website, our team is ready to help.

When performance matters, and every connection counts, Fasto is the partner you can rely on.

📧 info@fasto.cn
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