Radius of Pitch Circle of Pinion is the distance from the center of the pinion to the pitch circle, where the gear teeth engage with the teeth of a mating gear. And is denoted by r. Radius of Pitch Circle of Pinion is usually measured using the Millimeter for Length. Note that the value of Radius of Pitch Circle of Pinion is always negative. Typically, the value of Radius of Pitch Circle of Pinion is greater than 0.