What Is Galling (Thread Seizure)?
Galling — also known as thread seizure or cold welding — is a condition where a bolt and nut fuse together during tightening, making it impossible to advance or remove the fastener. The result is a permanently locked assembly that often requires destructive removal. Galling has long been one of the most persistent challenges in the stainless steel fastener industry.
Why Does Galling Occur in Stainless Steel Fasteners?
Galling is significantly more common in stainless steel than in carbon steel, and occurs due to two primary factors:
Material Characteristics
Austenitic stainless steel (300-series) has excellent corrosion resistance, but its material properties make it inherently prone to galling. The alloy is relatively soft, has a high coefficient of friction, and lacks the natural lubricity of carbon steel. Under contact pressure and rotational friction, the oxide layer on mating thread surfaces breaks down, causing direct metal-to-metal contact. The resulting heat and pressure trigger micro-welding at the thread interface — this is galling.
Improper Installation Practices
Even with correct material selection, poor installation technique significantly increases galling risk. Common causes include:
- Tightening too fast, especially with power tools, generating excessive frictional heat
- Misaligned threads or cross-threading at the start of engagement
- Contaminated or damaged threads that increase contact resistance
- Excessive torque beyond the safe tightening range
- Applying force at an angle rather than perpendicular to the bolt axis
High-Risk Applications
Galling is particularly prevalent in demanding environments where fasteners are subject to high loads, vibration, or rapid installation. Common high-risk sectors include:
- Railway infrastructure — high-vibration environments with frequent maintenance cycles
- Curtain wall and facade systems — stainless fasteners under sustained tension and thermal cycling
- Flange connections — high bolt loads in piping and pressure vessel assemblies
- Elevated and aerial work — where fastener removal after seizure is hazardous
- Power tool assembly — high-speed installation that generates rapid frictional heat
How to Prevent Galling
1. Use Anti-Galling Nuts for High-Risk Applications
For applications in the sectors listed above, FULLERKREG recommends specifying anti-galling nuts engineered to minimize thread friction and prevent micro-welding. These products have been validated in real-world applications and are recognized for their effectiveness in high-risk environments, including railway infrastructure certified by quality inspection authorities.
2. Follow Correct Installation Procedures
Proper technique is essential regardless of fastener grade:
- Select the correct bolt length: After full tightening, 1–2 thread pitches should protrude beyond the nut face.
- Verify load ratings: Ensure the bolt tensile strength and nut load capacity meet design requirements.
- Keep threads clean: Remove any contamination or debris before assembly. If thread damage is present, the nut must at minimum pass freely by hand before tightening.
- Apply force perpendicular to the bolt axis: Never tighten at an angle — this causes uneven thread contact and dramatically increases galling risk.
- Use a calibrated torque wrench: Apply torque within the safe range specified for the fastener size (refer to product packaging). Apply force smoothly and evenly throughout the tightening stroke.
Why Specify FULLERKREG Anti-Galling Nuts?
FULLERKREG supplies anti-galling stainless steel nuts engineered for demanding applications. Key advantages include:
- Proven field performance: Validated by extensive real-world use across multiple industries, with consistently superior anti-galling results compared to standard stainless nuts.
- Railway-certified: Tested and recognized by railway industry quality inspection authorities for effective prevention of thread seizure.
- Easy installation: No special tools or procedures required. Suitable for operating temperatures from −30°C to +100°C. Simply ensure correct product selection and basic installation alignment.
- Patented technology: Proprietary design protected by national invention patent, representing leading domestic technical capability.
- RoHS compliant: Meets EU RoHS environmental requirements for restricted substances.
FULLERKREG Technical Support
Not sure whether your application is at risk for galling? Our engineering team can assess your use case and recommend the appropriate specification — whether standard stainless nuts, anti-galling nuts, or an alternative grade such as 316 or duplex stainless.
Contact FULLERKREG for product selection guidance, bulk pricing, and technical documentation.