Garnett wire

It is a toothed bar or rod that can be thought of as a sector gear

with an infinitely large radius of curvature. Torque can be converted

to linear force by meshing a rack with a pinion: the pinion turns; the

rack moves in a straight line. Such a mechanism is used in automobiles

to convert the rotation of the steering wheel into the left-to-right motion

of the tie rods.

Gear geometry, for instance, the tooth shape of an interchangeable set

of gears may be specified for the rod and the tooth shapes for gears of

particular actual radii then derived from it. The rack and pinion gear type

is employed in a rack railway.