Fretting is considered as a type of wear that occurs in the presence of a small movement between machine components. The small movement could be observed in parts that are not intended to move, and also parts where limited movement is allowed by design. Bolted joints, hollow-bore-shaft mating area, keyways, turbine blade roots, bearing races, shrink fitted and press fitted parts are examples of where unintended movement occurs. And flexible coupling, splines, cams, leaf springs are components that are allowed to have limited internal movement.