A collet is a sleeve with a cylindrical inside and a conical outside. The collet has kerf cuts along its length to allow it to expand and contract. A threaded section at the rear of the collet is used to pull it into a matching conical socket. As the collet is pulled into the socket, the collet will contract - gripping the contents of the inner cylinder. Collets are most commonly found on milling machines, lathes, wood routers, and precision grinders. Collets can also be obtained to fit Morse or Brown and Sharpe taper sockets.

Typically collets offer far higher levels of precision and accuracy than self-centering chucks, and have a far shorter setting up time than independent-jaw chucks. The penalty is that most collets can only accommodate a single size of workpiece. An exception is ER collets which typically have a working range of 1mm. Air cylinders or collet chucks are made to hold cylindrical work, but are available to hold square, hexagonal or octagonal work pieces.