Tool Cone

a conical tool shank (stem) or cradle in the spindle of a machine tool or instrument; it is used for connecting drills, reamers, countersinks, other tools, and mandrels (chucks) and centers to the spindles of machine tools and instruments. A tool cone provides rapid and convenient fastening, precision centering, and reliable operation of a tool, and it facilitates inter-changeability. Tool cones are standardized in the USSR.