Collets are specialized sleeve bushings that fit into collet chucks or machine spindles to hold small-diameter tool shanks, such as end mills or bits. They firmly grip the cutting tool to prevent it from wobbling or loosening during machining. Collets also center the cutting tool in the spindle to enhance cutting accuracy, repeatability, and concentricity. Collets are used on milling machines, lathes, grinders, and other machine tools.