Galling and Seizing

We get questions about galling or seizing. The customer’s complaint is that during installation the bolts are twisting off and/or the bolt’s threads are seizing to the nut’s thread. Often the customer thinks there is a quality issue. Leading the customer to believe this is a product quality issue.

The problem is most likely “thread galling.” According to the Industrial Fastener Institute’s 6th Edition Standards Book:

"Thread galling seems to be the most prevalent with fasteners made of stainless steel, aluminum, titanium, and other alloys which self-generate an oxide surface film for corrosion protection. During fastener tightening, as pressure builds between the contacting and sliding thread surfaces, protective oxides are broken, possibly wiped off, and interface metal high points shear or lock together. This cumulative clogging-shearing-locking action causes increasing adhesion. In the extreme, galling leads to seizing – the actual freezing together of the threads. If tightening is continued, the fastener can be twisted off or its threads ripped out."

Possible Resolutions

• Use Dissimilar Stainless Steel

  Depending on your application mating of materials of different hardness could solve your troubles. If one of the components is 316 and the other is 304 they’re less likely to gall. Be aware of end use.

• Anti-Seize Lubricants

  This process eliminates thread galling. Extreme pressure waxes or lubricants that contain molybdenum disulfide), graphite, mica, or talc. Before use you should be aware of the end use of the fasteners.

• Slow Down Installation

  By reducing the speed of installation you may solve the problem. As the installation speed increases, the heat generated increases increases. As heat increases the tendency for thread galling occurs.