Causes may include imbalance in the moving parts of plant & equipment, and external forces due to the normal operation of commercial vehicles both on- and off-roads, trains on tracks, aboard ships etc.

Vibrations, to quickly move back and forth (or up and down) about a point of equilibrium. Vibration may be periodic (having a pattern) or random.

Did you know that the Junker test is the most severe vibration test for bolted connections? The bolted joint is exposed to transverse movements underneath the bolt head or nut, while the clamping force is continuously measured. The effectiveness of different locking methods can easily be compared.