A linear actuator includes: a screw shaft that has a screw thread and a longitudinal axis A and a nut movable along the screw shaft from a retracted position to an extended position. The actuator also includes a plurality of rollers movable with the nut, each of which includes a cylindrical surface configured to roll along one or more flanks of the screw thread, such that rotation of the screw shaft causes the rollers to roll along the flank(s) so that the nut translates in an axial direction along the screw shaft. The screw thread includes one or more detents (e.g., grooves) configured to lock the nut in one or more axial positions.