Counterbores

Counterbore, or counterbore cutters, are drill-bits used to make counterbore holes, which is a way of creating a flat-bottomed extension of an existing hole in a material. The counterbore cutter will essentially create a cylindrical cavity at the head of an already drilled hole. This allows the hole to accommodate flat bottomed screw or bolts so that they sit flush to the surface of the materia...