Thread Galling

Thread galling is a form of adhesive wear where the threads of a fastener and its mating part seize and tear due to metal-to-metal contact under pressure. As the bolt or screw turns, friction and heat can cause microscopic high points on the thread surfaces to cold-weld together, then rip apart, leaving rough, smeared material on the threads. Galling is most common with stainless steel fasteners (especially stainless-on-stainless), but it can also occur with aluminum, titanium, and other materials prone to adhesive wear, particularly when the materials are similar in hardness and the assembly is tightened quickly.

Galling can show up as sudden binding during tightening, a fastener that locks up before reaching torque, or threads that strip or break when you try to remove them. To reduce the risk, use lubrication or anti-seize compounds, choose coatings or plated finishes designed to lower friction, and consider pairing dissimilar materials (for example, a stainless bolt with a different nut material or a coated nut). Slowing installation speed, avoiding over-torquing, and using proper torque values and washers can also help by reducing heat and thread pressure, which are key drivers of galling.