A chuck is a specialized type of clamp

Clamp (tool)

A clamp is a fastening device to hold or secure objects tightly together to prevent movement or separation through the application of inward pressure...

 used to hold an object, usually an object with radial symmetry

Rotational symmetry

Generally speaking, an object with rotational symmetry is an object that looks the same after a certain amount of rotation. An object may have more than one rotational symmetry; for instance, if reflections or turning it over are not counted, the triskelion appearing on the Isle of Man's flag has...

, especially a cylindrical

Cylinder (geometry)

A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...

 object. It is most commonly used to hold a rotating tool (such as the drill bit

Drill bit

Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....

 in a power tool

Power tool

A power tool is a tool that is actuated by an additional power source and mechanism other than the solely manual labour used with hand tools. The most common types of power tools use electric motors. Internal combustion engines and compressed air are also commonly used...

) or a rotating workpiece (such as the bar

Bar stock

Bar stock, also colloquially known as billet, is a common form of raw purified metal, used by industry to manufacture metal parts and products....

 or blank in the headstock spindle

Spindle (tool)

In machine tools, a spindle is a rotating axis of the machine, which often has a shaft at its heart. The shaft itself is called a spindle, but also, in shop-floor practice, the word often is used metonymically to refer to the entire rotary unit, including not only the shaft itself, but its bearings...

 of a lathe

Lathe (metal)

A metal lathe or metalworking lathe is a large class of lathes designed for precisely machining relatively hard materials. They were originally designed to machine metals; however, with the advent of plastics and other materials, and with their inherent versatility, they are used in a wide range of...

). Some chucks can also hold irregularly shaped objects (ones that lack radial symmetry). In some applications, the tool or workpiece being held by the chuck remains stationary while another tool or workpiece rotates (for example, a drill bit in the tailstock spindle of a lathe, or a round workpiece being milled by a milling cutter

Milling cutter

Milling cutters are cutting tools typically used in milling machines or machining centres . They remove material by their movement within the machine or directly from the cutter's shape .-Features of a milling cutter:Milling cutters come in several shapes and many sizes...

).

Many chucks have jaws, which are dogs

Dog (engineering)

In engineering a dog is a tool that prevents movement or imparts movement by offering physical obstruction or engagement of some kind. It may hold another object in place by blocking it, clamping it, or otherwise obstructing its movement...

 that are arranged in a radially symmetrical pattern (like the points of a star

Star (symbol)

A star is an ideograph whose outer edge forms a symmetrical polygon whose vertices alternate between joining outward- and inward-pointing pairs of edges. The figure may be the border or interior of the polygon, or one or more closed polygonal paths that include all of the border and also have some...

) to hold the tool or workpiece.