Collet sets come in a variety of sizes and comprise many collets of the same design. When switching between multiple tool sizes on the same machine, they help speed up tool changes. Collets are specialized sleeve bushings that retain small tool shanks or workpieces in collet chucks or machine spindles. They maintain a solid grip on the tools and workpieces during machining to prevent them from wobbling or loosening. To increase cutting precision and concentricity, they also center tools and workpieces. Milling machines, lathes, grinders, and other machine tools all employ collets.