It is a small cogwheel. The teeth fit into a larger gear wheel.
Rotational motion is converted into linear motion when the pinion turns
and moves the rack. Pinion gears are engineered to be the best gears. Pinion gear system involves the use of a small round gear called pinion and a large flat gear called rack, more the number of teeth in the pinion gear, more is the speed of rotation. Pinion with smaller number of teeth produces more torque. Pinion is attached to the motor shaft with glue. Rotation of pinion is done by rotation of pinion about a fixed center that helps the rack to move in the straight line. If the rack is moved and the pinion rotates then the center of the pinion moves taking along the pinion with it.