Steel

Iron mixed with a small amount of carbon. Watchmakers refer to a watch's steel components (rocker, screws, index, etc.) as "steels". Among the different grades of steel, semi-hard is used for transmission arbors, embossed or bent parts. Hard steel is used for screws, pinions and watch parts that do not require very hard grade steel. Very hard and extra hard steel is used for springs, files and suchlike.