An ER11 Collet Package (1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm) is a set of thirteen collets that can hold different sizes of tools in CNC machines, such as engraving machines, milling machines, or lathes. collet is a type of collet that has a cylindrical body with slits along the length that allow it to expand and contract. collet can grip the tool securely and accurately by applying a clamping force through a nut or a drawbar.