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 are used for geological work, where a deep hole is drilled in sediment or ice and the drill bit, which now contains an intact core of the material drilled with a diameter of several centimeters, is retrieved to allow study of the strata. A countersink is a conical hole cut into a manufactured object; a countersink bit (sometimes called simply countersink) is the cutter used to cut such a hole. A common use is to allow the head of a bolt or screw, with a shape exactly matching the countersunk hole, to sit flush with or below the surface of