Many mechanics are specialized in a particular field such as auto mechanics, truck mechanic, 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, on the other hand, has a wide variety of topics to learn. A mechanic is typically certified by a trade association or regional government power. There are different types of mechanics: heavy weight and light weight. Heavy weight work is on bigger machines like tractors and trailers; light weight work on smaller items like engines for a car.