The rocking-bar is moved by a rack g into which a pinion on a cross-spindle j gears; the cross-spindle is moved by means of a worm-wheel into which a worm on the longitudinal FIG.
The worm-wheel shaft then sometimes carries a spur-pinion gear ing with a spur-wheel on the lifting shaft, whereby a much greater mechanical advantage is obtained with a small loss by friction of the spur gearing.
This rod turns a worm-screw which acts on a worm-wheel fitted " spring tight " upon the axis of the micrometer-screw.
