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There are essentially three types of drill rod classified in the way they are hardened. These are water hardening, oil hardening and air hardening. The reasons for selecting one over the other have to do to various factors such as material cost, development of cracks during the heat treatment process, sensitivity to distortion, resistance to decarburization and various other factors. The more common types are W1, O1 and A2. W1 is the least expensive but is the most prone to microcracking and dimensional distortion. This is mainly due to the abrupt temperature change during quenching in water. This steel is generally used for low precision applications such as knives, scissors, tweezers etc. O2 is subjected to less shock during quenching due to the fact that it is quenched in oil and changes temperature more slowly. It is therfore less prone to micro cracks and has better dimensional stability than water hardening steels. Oil hardening steels are used for drill bits, end mill cutters, and other precision cutting tools. A2 is by far the most expensive and costs about three times the price of the water hardening steels. The hardening process involves heating the part to a cherry red and simply letting it cool in the air. This minimizes the shock of abrupt temperature changes during quenching. It is used in applications where micro cracks and dimensional instability are unacceptable. A2 is used in products such as stamping dies and other products requiring high stability after heat treating. A 1/4 inch diameter rod that is three feet long costs about $10.00 from MSC and would probably last most watch and clock makers several years of pivoting.