A jack extension tube preferably for vehicles is provided which comprises an elongated tube with a threaded nut securely mounted therein, and a jack screw received in an open end of the tube and threadably received in the threaded nut. The tube has a first flange extending inwardly adjacent an inner end of the threaded nut and a second flange extending inwardly adjacent an outer end of the threaded nut whereby the threaded nut is securely retained within the elongated tube between the first and second flanges. The threads on the threaded nut can be involute threads to reduce noise, wear and chucking between the nut and the screw. The threaded nut can be formed of a rigid synthetic resin material. Further, a stop can be provided on one of the jack screw inner end and the threaded nut inner end whereby the stop prevents the threads on the jack screw from being separated from the threads on the threaded nut during rotation of the jack screw relative to the threaded nut and allowing for a low starting torque when the screw is rotated in a reverse direction.