Linear actuator for providing rotational movement into linear movement and vice versa, the linear actuator comprising: - a piston rod; - an outer ball lead-screw with internal helical ball rolling grooves; - an inner ball lead-screw body having outer helical ball rolling grooves and deflector channels; - the outer ball lead-screw is rotated to laterally move the inner ball lead-screw body through a plurality of balls in rolling contact with the outer ball lead-screw and the inner ball lead-screw body to transfer the load and to achieve lateral movement of the piston rod of the linear actuator; - the inner ball lead-screw body with deflector channel between two helical ball rolling circuits communicating with each other as the recirculation groove gradually slopes into a diameter slightly larger than the ball before entering into the deflector channel where the deflector groove is deep enough for the balls to pass unimpeded over the land between the adjacent grooves of the outer ball lead-screw; and - the number of helical ball rolling grooves on the outer ball lead-screw is giving the lateral stroke of the piston rod, Characterised by; - the outer ball lead-screw rotates and is threadingly engaged with the inner ball lead-screw body through the plurality of balls; - the inner ball lead-screw body is fixed to the piston rod and is moved laterally by the plurality of balls between the outer ball lead-screw and inner ball lead-screw body; - the deflector channel between each ball recirculation circuit on the inner ball lead-screw body, wherein adjacent deflector channels are circumferentially evenly spaced apart on the inner ball lead-screw body: - the deflector channel is formed in a way that prevent the balls to fall out of the deflector channel when passing over the land between the adjacent grooves of the outer ball lead-screw; and - at least one protruding rod. - an outer ball lead-screw with internal helical ball rolling grooves; - an inner ball lead-screw body having outer helical ball rolling grooves and deflector channels; - the outer ball lead-screw is rotated to laterally move the inner ball lead-screw body through a plurality of balls in rolling contact with the outer ball lead-screw and the inner ball lead-screw body to transfer the load and to achieve lateral movement of the piston rod of the linear actuator; - the inner ball lead-screw body with deflector channel between two helical ball rolling circuits communicating with each other as the recirculation groove gradually slopes into a diameter slightly larger than the ball before entering into the deflector channel where the deflector groove is deep enough for the balls to pass unimpeded over the land between the adjacent grooves of the outer ball lead-screw; and - the number of helical ball rolling grooves on the outer ball lead-screw is giving the lateral stroke of the piston rod, - the outer ball lead-screw rotates and is threadingly engaged with the inner ball lead-screw body through the plurality of balls; - the inner ball lead-screw body is fixed to the piston rod and is moved laterally by the plurality of balls between the outer ball lead-screw and inner ball lead-screw body; - the deflector channel between each ball recirculation circuit on the inner ball lead-screw body, wherein adjacent deflector channels are circumferentially evenly spaced apart on the inner ball lead-screw body: - the deflector channel is formed in a way that prevent the balls to fall out of the deflector channel when passing over the land between the adjacent grooves of the outer ball lead-screw; and - at least one protruding rod.