An ER collet is a type of clamping device used in machining and manufacturing to hold tools or workpieces securely. It consists of a cylindrical sleeve with a series of slots that allow it to expand and contract when tightened or loosened. This design provides a strong grip on various tool shanks, ensuring precision during operations like milling or drilling. ER collets are available in different sizes and can accommodate various tool diameters. They are commonly used in conjunction with collet chucks and are favored for their versatility and ease of use. This makes them essential components in many CNC (Computer Numerical Control) machines.