筒夹是一种零件，它主要负责把小直径的工作物夹紧于主轴端。主要用于六角车床及自动车床。

依种类可分为：

• 车床筒夹
• 六角筒夹
• 5c筒夹
• 套筒夹头
• 精密筒夹

维基共享资源中相关的多媒体资源：筒夹

• Hoffman, Edward G., Jig and fixture design 5th, Cengage Learning, 2004, ISBN 9781401811075. 

A collet /ˈkɒlᵻt/ is a subtype of chuck that forms a collar around an object to be held and exerts a strong clamping force on the object when it is tightened, usually by means of a tapered outer collar. It may be used to hold a workpiece or a tool.

An external collet is a sleeve with a (normally) cylindrical inner surface and a conical outer surface. The collet can be squeezed against a matching taper such that its inner surface contracts to a slightly smaller diameter, squeezing the tool or workpiece whose secure holding is desired. Most often this is achieved with a spring collet, made of spring steel, with one or more kerf cuts along its length to allow it to expand and contract. An alternative collet design is one that has several tapered steel blocks (essentially tapered gauge blocks) held in circular position (like the points of a star, or indeed the jaws of a jawed chuck) by a flexible binding medium (typically synthetic or natural rubber). The Jacobs Rubber-Flex brand is a name that most machinists would recognize for this type of collet chuck system. Regardless of the collet design, the operating principle is the same: squeeze the collet against the tool or workpiece to be held, resulting in high static friction. Under correct conditions, it holds quite securely.