which, once clamped by the mounting screws, cannot allow relative slipping between the two parts. Collet A collet, one type of chuck, 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 radially against the tool or workpiece to be held, resulting in high static friction. Under correct conditions, it holds quite securely. Almost all collet chucks achieve the radial squeezing motion via moving one or more male-female pairs of tapered (conical) surfaces axially, which produces the radial squeezing in a highly concentric manner. Depending on the collet design, it can be either pulled (via a threaded section at the rear of the collet) or pushed (via a threaded cap with a second taper) into a matching conical socket to achieve the clamping action. As the collet is forced into the tapered socket, the collet will contract, gripping the contents of the inner cylinder. (The axial movement of cones is not mandatory, however; a split bushing squeezed radially with a linear force—e.g., set screw, solenoid, spring clamp, pneumatic or hydraulic cylinder—achieves the same principle without the cones; but concentricity can only be had to the extent that the bushing's diameters are perfect for the particular object being held. Thus only in toolroom contexts, such as machine tool tooling creation and setup, is this common.) One of the corollaries of the conical action is that collets may draw the work axially a slight amount as they close. Collet chuck systems that make no provision to prevent this draw-in are often called draw-in collet chucks, in contrast to systems which circumvent this