Drill bit shank shaft and shank, is usually of the same diameter. It is held usually in a three-jaw drill chuck. Bits of diameter too small to grip firmly can have straight shanks of larger diameter than the drill, which can be held firmly in a standard size collet or chuck. Large drill bits can have straight shanks narrower than the drill diameter so that they can be fitted in chucks not able to chuck the full diameter. Such a drill bit is called a reduced-shank or blacksmith's drill. For example, this allows a bit to be used in a pistol-grip drill's chuck.
Drill bit (well) easily "steered" during drilling has become a third, possibly driving, primary goal of the design. The ability of a bit design to satisfy the two primary goals is constrained by a number of factors, most importantly the wellbore diameter. Other constraints are dictated by its intended use: formation type (hardness, plasticity, abrasiveness) to be drilled, operating environment at depth (temperature, pressure, corrosiveness), the capabilities of the equipment used in the operation (rotating speed, available weight on bit, pump horsepower) and the angle of the wellbore (vertical, directional, horizontal). Modern drill bit designs try to balance these constraints to achieve the