"Servo gears" can refer to gears inside of the servo or a gear that goes on the output spline of the servo. Gears inside of the servo are driven by the motor and there are typically several stages that each act to reduce the speed and increase the torque. These gears come in many different materials, such as but not limited to nylon, Karbonite, aluminum, brass, steel and titanium. When the phrase 'servo gear' refers to a gear that goes onto the output spline of the servo, the gear will have a bore that needs to match the spline type of the servo it is to be installed on. This servo gear typically mates to a hub gear in order to create a ratio between the servo and the driven shaft to change the torque and the speed at that driven shaft.