The collet system, that anyone who has used a router will be familiar with, is one of the simplest and arguably best chucking systems. A collet based chuck system generally comprises three parts, an outer tapered receiving sleeve that the collet sits in, a collet and a tightening nut.

There are hundreds of different designs of collet but they all work along the same principal of compressing the collet around the shank of the tool. The collet, which is usually made of spring steel and has three vertical slits cut into it (kerfs), sits in the tapered receiving sleeve and the tightening nut is screwed around the outside of the assembly. The tightening nut normally screws onto the outside of the receiving sleeve and is designed to force the collet into the sleeve as the nut is done up. Since the receiving sleeve is tapered as the collet is forced into the sleeve the slits cut into it close up. By this action the collet can compress around the shank of a tool and hold it firm.

A less common way of compressing the collet is to thread the end of the collet and pull it into the receiving sleeve. This has the advantage of not requiring a tightening nut but is more complicated to produce.

Collets generally have a very narrow range of sizes that they will clamp and are made to fit a particular size of shank. For example, routers in Europe use 6mm collets where as in the US and UK ¼ inch is common (¼ inch is 6.35mm). A 6mm collet will not hold a ¼ inch bit nor will a ¼ inch collet reliably hold a 6mm bit. This clearly shows collets Achilles heal - the fairly high capital cost of needing to own numerous collets and long set up times if collets need to be changed on a regular basis.

On the plus side, if repetitive work is to be carried out which requires frequent tool replacement or all the bits have the same shank diameter then the collet chucking system is hard to beat in terms of speed and reliability.

As well as chucking speed, collets also offer excellent centring precision and self centring which is vital if accurate work is to be carried out. They also provide a good clamping force and are difficult to vibrate loose.

Collet chucks are very extensively used in metal work and come in thousands of different shapes and sizes. There are a few standard collets but many tool manufactures produce collets that are designed specifically for their own tools (arguably as a form of vendor lock in). Collet sizes vary from a millimetre or less up to tens of centimetres and while generally designed to grip a round bar also exist to grip bars of other shapes such as square and hexagonal. Woodworkers will be most familiar with collet chucking systems from work with rotary tools (such as the Dremel) and routers.