An actuator which is operable in response to one of an electrical and an electro-mechanical input signal is provided. The actuator includes an outer casing defined about a central axis, an output shaft disposed within the casing, the output shaft being axially moveable over a stroke length. Further, the actuator also includes a drive mechanism co-operable with the output shaft to drive the output shaft along a part of the stroke length, wherein the actuator is configured such that the output shaft is drivable along all or part of the remainder of the stroke length by external loading while being unconstrained by the drive mechanism.
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