Gears have been around for a very long time. It is generally understood that gears were invented by the Greek mechanics of Alexandria in the third century B.C., were further developed by Archimedes, and saw wide use in the Roman empire.
Gears and gearbox configurations come in many shapes and sizes, not to mention materials, tooth profiles and accuracy standards. Accordingly, there is a range of different materials and manufacturing techniques that can be used. Selecting the correct materials, gear designs and accuracy standards are not only critical to gear performance, but also can significantly affect cost. Over specifying a gear will incur unnecessary cost, under specifying a gear will result in under performance in the form of inadequate gear life or catastrophic failure.
