A pinion gear is a small gear that engages with a larger gear, known as a crown gear or rack, to transmit motion and force in mechanical systems. It is commonly used in various applications, such as in vehicles, machinery, and clocks, to convert rotational motion into linear motion or to change the direction of movement. Pinion gears are essential components in gear trains, where they help to increase torque or change speed. They are typically made from durable materials like steel or plastic, ensuring longevity and efficiency in their operation. Proper alignment and sizing of the pinion gear are crucial for optimal performance in any system.