A drill bit is the actual device that excavates the rock from the bottom of the well as it is being drilled. Drill bits come in many sizes, types, and shapes and are designed to drill all types of rocks. There are four main types of drill bit used today: Milled Tooth, Tungsten Carbide Insert (TCI), Poly Diamond Crystalline (PDC), and Diamond Bits. Each is used for particular rock types. Milled tooth bits are the cheapest and diamond or diamond enhanced bits are the most expensive. A milled tooth bit is composed of three “cones” on which are many steel “teeth” that dig into soft rock and scraped the rock away to make a hole. They wear out quickly but drill quickly. A TCI bit is composed of three cones, on which are many tungsten carbide “inserts” or little ice cream cone-shaped buttons. These buttons drill by crushing the rock and pushing it out of the way. A PDC bit does not have cones but is a solid, fire hydrant-shaped block of steel with a flat bottom surface. On this flat surface are many small diameter (/2” to ¾” diameter) wafers made of a poly diamond crystalline substance. These wafers are positions on the flat surface so that they will scrape the rock very lightly to drill. The bit is rotated very fast and a large volume of fluid is circulated through the PDC bit keep it cool and to remove the scraped particles of rock. A diamond bit is used in very hard rocks that require a long period to time to grind away the rock. Diamond bits typically drill very slow and are used a last resort to drill hard rocks. PDC bits are currently used widely due to the faster drilling rates these bits can deliver. Drill bits are purchased by the operating company, not the drilling contractor. They are expendable and use “until destroyed.” There is not a “perfect” drill bit and the technology is constantly changing to get better drill bit performance. Major manufacturers of drill bits are Smith International, Hughes Tool Company, Security Drill Bits (owned by Halliburton), Varel Drill Bits, and Reed Bits (owned by GrantPrideco).