Tower Pro SG90 is an ideal servo motor for little mechanism. You may conveniently use it in your projects or RC vehicles. Additionally it works with PWM signal can be generated by a microcontroller or Arduino. This means you can use is in your robotics projects too.
It has a plastic gear box. The servo comes with servo horns and the other additional parts. Rotating the motor shaft by hand like the other servos may harm the gears of this servo. You should avoid of this response.
If you’re looking for more Rack and Pinion Gear options, check this collection