Abstract: A miniature or subminiature, rectangular potentiometer which automatically disengages and engages at the extreme end settings may be fabricated by using a worm screw which engages and disengages a sector gear. The sector gear is arranged and configured to selectively engage a spring at the extremes of travel of the sector gear. When the worm screw drives the sector gear to the limit of its travel, the spring is compressed against the gear thereby compressing the spring. The compression of the spring is sufficient to permit the gear teeth on the opposing end of the sector gear to advance and disengage from the worm screw. Rotation of the worm screw in the opposing direction automatically re-engages the sector gear by virture of the urging of the spring.