A collet is a steel sleeve which holds a bit in the router. The collet works with the router shaft which is connected directly to the motor and the collet nut. Different machines may use different collets; Consult your owner's manual, check with your machine's manufacturer, or give us a call to see which collet is right for you and your machine. We keep a large selection in stock and on hand to get you the tools you need in a timely manner.