What is the effect of using lubricants on bolt threads when measuring clamping force?

Using lubricants on bolt threads primarily affects the friction between the bolt and the material it is being tightened against. When you apply a lubricant to the threads, it reduces the amount of friction encountered during the tightening process. This reduction in friction means that a greater portion of the applied torque is converted into clamping force, rather than being lost to overcoming thread friction.

Therefore, with the reduced friction due to lubrication, the effective clamping force is increased, leading to a more efficient and reliable connection. This is why it is common practice to lubricate threads in many applications to achieve a specified clamping force with greater ease and consistency. Accurate torque readings will yield more reliable clamping force because the lubricant allows for greater efficiency in torque transmission.

In contrast, without lubrication, more torque is required to achieve the same clamping force due to the higher friction levels. Hence, using lubricants fundamentally enhances the effectiveness of the fastening by ensuring that the applied torque is translated more effectively into clamping force.