Collets are used to hold a tool in a central position as it rotates. As the tool is inserted into the collet, the device expands and provides uniform pressure that holds the tool in place. However, if the collet stretches too far, it cannot secure the instrument properly and may lose shape.

A collet resembles a segmented metal band or sleeve. It is designed to fit around a cylindrical object and apply equal pressure to its entire circumference. However, some collets are made to fit hexagonal, square, octagonal and round work pieces and tools.

A collet is a form of chuck, but it is not identical. While a chuck is tightened around an object, a collet utilizes clamping pressure by forming a collar around the object being held, holding it securely in place.