Torsion is the twisting or wrenching of a body by the exertion of forces tending to turn one end or part about a longitudinal axis while the other is held fast or turned in the opposite direction.

Torsion is a typical load to which components are subjected. The resultant stresses and deformations can lead to failure of the component. A number of different factors play a role in this, including the material, the cross-section of the bar, the clamping length and the method of bearing support.