Milling is a machining operation that removes material off the surface of a piece of stock using a revolving milling tool. Parts with a variety of shapes and features, such as pockets and slots, are made using it. To execute milling activities, milling tools are mounted on a CNC (computer numerical control) or manually driven milling machine. End mills are used to make items with complex forms and profiles and have cutting edges on its nodes and sides. Internal and exterior threads are formed on existing holes by thread mills. Keyseat cutters carve grooves in shafts so that keyed pieces can be mated to them. Mold and die milling tools are used to make molds and dies and have tapered sides. Letters, numerals, and designs are carved out of parts using engraving equipment. To create decorative edges and other characteristics, router bits remove material from workpieces.