A collet is a holding element - a type of chuck that forms a collar around the workpiece being held and generates a strong clamping force around it. It can be used to hold both the workpiece and the tool.

The inner collet is a sleeve that has a cylindrical inner side and a tapered outer side. The sleeve can be clamped around a matching cone - the inner side shrinks to a slightly smaller diameter, securely clamping the tool or workpiece. This is accomplished most often with resilient bushings, made of spring steel, which have one or more notches along their length, allowing the sleeve to expand and contract. An alternative to this design are bushings that have several tapered steel plates forming a circle, held together by a flexible material (usually natural or synthetic rubber). A brand name for this type of collet is Jacobs Rubber-Flex collets. Regardless of the design of the collet, the principle of its operation remains the same: clamping the collet around a tool or workpiece.



On milling machines (hand-held or bench-top), the collet holds the drill/router/tool in place. In the U.S., these tools are usually 6.4 or 12.7 mm shanks, while in Europe the most common sizes are 6 or 8 mm. The bushing is hexagonal on the outside, allowing it to be tightened or loosened with a standard wrench.


tuleja automatowa DIN6343

There are many types of collet used in the metalworking industry. Common industry-standard designs are R8 (internally threaded for mills) and 5C (usually externally threaded for lathes). There are also proprietary designs which only fit one manufacturer's equipment. Collets can range in holding capacity from zero to several inches in diameter. The most common type of collet grips a round bar or tool, but there are collets for square, hexagonal, and other shapes. In addition to the outside-holding collets, there are collets used for holding a part on its inside surface so that it can be machined on the outside surface (similar to an expanding mandrel). Furthermore, it is not uncommon for machinists to make a custom collet to hold any unusual size or shape of part. These are often called emergency collets (e-collets) or soft collets (from the fact that they are bought in a soft (unhardened) state and machined as needed). Yet another type of collet is a step collet which steps up to a larger diameter from the spindle and allows holding of larger workpieces. In use, the part to be held is inserted into the collet and then the collet is driven (using a nose cap) or drawn (using a drawbar) into the body which has a matching taper. When properly tightened, enough force is applied to securely clamp the workpiece or tool.


ER collets

tulejka zaciskowa ER collet

The "ER" collet system, developed and patented by Rego-Fix in 1973, is the most widely used collet system in the world and is now available in the product range of many companies worldwide. The standard sizes are ER-8, ER-11, ER-16, ER-20, ER-25, ER-32, ER-40 and ER-50. The name "ER" comes from the pre-existing "E" sleeve modified by Rego-Fix, which added an "R" from its name. The number indicates the diameter of the sleeve at the face of the chuck given in millimeters. ER sleeves are also used in lathes to hold workpieces.

R8 collets

tulejka zaciskowa R8 collet

R8 collets were developed by Bridgeport Machines, Inc. for use in milling machines. Unusually, R8 collets fit into the machine taper itself (i.e. there is no separate chuck) and tools with integral R8 taper can also be directly fitted. R8 was developed to allow rapid tool changes and requires an exact match between collet and tool shank diameter.
R8 collets have a keyway to prevent rotation when fitting or removing, but it is the compressed taper and not the keyway that provides the driving force. Collets are compressed by a drawbar from behind, they are self releasing and tool changes can be automated.


5C collets

tulejka zaciskowa 5C

Unlike most other machine collet systems, 5C collets collets were developed primarily for work holding. Superficially similar to R8 collets, 5C collets have an external thread at the rear for drawing the collet closed and so work pieces may pass right through the collet and chuck (5C collets often also have an internal thread). Collets are also available to hold square stock. 5C collets have a limited closing range and so shank and collet diameters must be a close match.


Morse taper collets

tulejka zaciskowa Morse collet


Modeling and other hobbies

tulejka zaciskowa dremel collet

Many users (hobbyists, graphic designers, architects, students, etc.) are familiar with bushings, which are part of X-Acto and similar blade-holding knives. Another popular example are bushings holding replacement parts of Dremel and similar rotary files.