🔩 Why does bolt tightening waste 90% of the torque?

Added: 2026-05-25

[00:00:00]Tightening torque is a key indicator for controlling bolt clamping force.

[00:00:02]However, typically, 90% of the torque is consumed by friction with only 10% actually converted into clamping force.

[00:00:07]If the coefficient of friction is unstable, the clamping force generated by the same torque can fluctuate by more than double, directly affecting the safety of the fastener. So, what factors determine bolt torque distribution and the coefficient of friction? Ultimately, the change in the coefficient of friction is not accidental, but rather determined by the microscopic morphology of the contact surface. During tightening, a continuous dynamic evolution occurs, such as the shearing of surface roughness peaks, plastic deformation, and an increase in contact area. These physical changes directly alter frictional behavior, thus affecting torque conversion efficiency.