Why is lubrication applied to threaded fasteners during installation?

• A. To prevent galling, reduce installation torque variation, and facilitate future disassembly.
• B. To increase corrosion
• C. To keep threads from aligning
• D. To comply with color coding

Answer: (A)

Lubrication on threaded fasteners is used to control the friction in the threads so the torque you apply translates into a predictable clamping force. Without lubrication, high and erratic friction makes torque less reliable for achieving the correct preload, which can lead to over-tightening or under-tightening and uneven load distribution. A smooth lubricant reduces those variations, so the same torque provides a consistent grip.

Lubrication also helps prevent galling, which is a kind of seizing or cold-welding that can occur when metal surfaces rub together under pressure, especially with dissimilar metals or softer alloys common in aircraft joints. By reducing metal-to-metal friction, lubrication lowers the chance of that seizure and makes disassembly easier later on.

So the main benefits are a more predictable installation torque to clamp force, reduced risk of galling, and easier future disassembly. It isn’t about increasing corrosion, keeping threads from aligning, or color coding.