In order to cut a thread, a cylindrical bore must first be produced. The bore ends must now be deburred and converted into truncated cone surfaces before threading.
This process is usually referred to as countersinking and the tools as countersinks. The funnel-shaped countersinking facilitates the attachment of the tap. It should therefore be carried out before tapping. The further benefit of the countersinking process is to create space for the screw heads.
Since there are different screw heads, there are also differently fitting countersinks. A distinction is made between flat countersinks and flat countersinks and conical countersinks. The countersink produces a truncated cone for the so-called countersunk screws at a corresponding angle (90° cone head). The countersink produces a cylinder for the so-called cylinder head screws (hexagon socket screws).