Every motorized worm gear screw jacks must be controlled so that power to the motor is turned off and the brake engaged before the limits of mechanical travel are reached. JACTON limit switches senses extension shaft rotation and provides switch contact closures that can be used to control motors. JACTON limit switches is electromechanical device, directly installed on screw jack's protective tube, used for screw jack precision positioning travel limit and stop. Every motorized worm gear screw jacks has two limit switches, one is for lifting screw fully retracted travel, another for lifting screw full extend travel. At the bottom of lifting screw, will have a similar stop nut, when it touches limit switches' contacts, will break an electrical connection, then electric motor will be stop at the same time.