Why does lubrication affect torque readings, and how should you select a torque value for a lubricated fastener?

• A. Lubrication increases friction
• B. Lubrication lowers friction
• C. Lubrication has no effect
• D. Use dry torque regardless

Answer: (B)

The main idea is that torque readings depend on the friction inside the joint. Lubrication lowers that friction in the threads and under the bolt head, so more of the applied torque goes into stretching the bolt and creating clamping force rather than overcoming friction. Because of this, a lubricated fastener will develop a higher preload for the same torque than a dry one. To achieve the intended preload, you must use a torque value specified for the lubrication condition—usually smaller than the dry-torque value and based on the lubricant type, application, and surface finish. Always consult the lubrication-specific torque chart or manufacturer guidance; if that isn’t available, adjust the dry torque downward according to the approved factors and verify the resulting preload with the proper installation procedure.