Fastener preload
Also: bolt preload
Tension intentionally created in a fastener during tightening.
Preload compresses joint members and can resist separation or slip; tightening torque estimates it only indirectly through uncertain friction.
- Units
- newton (N)
- Formula
T ≈ KFd
Example 1.2 N·m on an M4 screw with K=0.20 estimates 1.5 kN preload.
Common misconception Higher tightening torque is not always safer and can yield threads or crush the joint.