curved rack

grabcad

People typically think of the rack as being the bar itself which has linearly aligned teeth to match up to other toothed bars on other devices that will pull or push on it using gears that work on an input power such as an electric motor. These days, a number of things exist that don't even involve electricity any longer at all since most rack and pinion setups just require someone physically turning one device while getting motion to do other stuff on another nearby.