#counterbore

• Countersink — A mechanical device, machinery, or tool mounted on a machine tool (such as a drill press or milling machine), used for widening, deepening, or calibrating holes previously executed in metal, wood, or plastic. As an adjective, it describes any factor, substance, mechanism, or instrument fulfilling the structural function of increasing depth.
• Countersink — Serving to deepen or to create a depression; a specialized tool, device, or mechanism used in mechanical workshops for enlarging, finishing, or structurally calibrating holes previously drilled in metal or wood pieces. In an adjectival or archaic sense, it describes an element that produces a deep penetration or causes an increase in the depth of a surface or geometric structure.