Pedal stops provide a reference point to stop the pedals from traveling too far. They also are used to reduce slack or excess travel. There are two basic pedal stop configurations: adjustable stops and fixed stops.
The adjustable stop typically uses an ADJUSTABLE set screw housed in a stop rail or bar. When the pedal rod activates the bell crank, the bell crank travels until it hits the screw which stops the travel. The amount of travel is adjusted by using the set screw to change the location of the stop in order to control the amount of pedal travel used.
The non-adjustable stop typically uses a FIXED stop of some type mounted to the front apron of the guitar. When the pedal rod activates the bell crank, the bell crank travels until it hits the stop which stops the travel. The amount of travel and slack are adjusted by using an adjustable screw to control the amount of return movement after activating the pedal.
The drawing below shows an example of an adjustable pedal stop: