Drill bit shank Drill bit shank The shank is the end of a drill bit grasped by the chuck of a drill. The cutting edges of the drill bit contact the workpiece, and are connected via the shaft with the shank, which fits into the chuck. In many cases a general-purpose arrangement is used, such as a bit with cylindrical shaft and shank in a three-jaw chuck which grips a cylindrical shank tightly. Different shank and chuck combination can deliver improved performance, such as allowing higher torque, greater centering accuracy, or moving the bit, but not the chuck, with a hammer action. This
Drill bit sizes size A (the smallest) to size Z (the largest). Although the ASME B94.11M twist drill standard, for example, lists sizes as small as size 97, sizes smaller than 80 are rarely encountered in practice. Number and letter sizes are commonly used for twist drill bits rather than other drill forms, as the range encompass the sizes for which twist drill bits are most often used. The gauge-to-diameter ratio is not defined by a formula, but is instead based on, but is not identical to, the Stubs Steel Wire Gauge, which originated in Britain during the 19th century. The accompanying graph,