A mechanic is a tradesman, craftsman, or technician who uses tools to build or repair machinery. Many mechanics are specialized in a particular field such as auto mechanics, bicycle mechanics, motorcycle mechanics, boiler mechanics, general mechanics, industrial maintenance mechanics (millwrights), air conditioning and refrigeration mechanics, aircraft mechanics, diesel mechanics, and tank mechanics in the armed services. Auto mechanics, for example, have many trades within. Some may specialize in the electrical aspects, while others may specialize in the mechanical aspects. Other areas include: brakes and steering, automatic or standard transmission, engine repairs or diagnosing customer complaints. An auto technician has a wide variety of topics to learn. A mechanic is typically certified by a trade association or regional government power.