Collet fixtures are tools used in machining operations to hold and secure workpieces. As an example,the 5C collet system is a popular standard for holding round workpieces in a lathe, milling machine, or other machining equipment.

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.