Countersink Reamer

a metal-cutting tool designed for finishing (countersinking) the walls of holes. Unlike a drill, a countersink usually has three to six cutting bits located obliquely or perpendicular (in face countersinks) to the shaft axis. Countersinks are manufactured as one-piece units from high-speed steel, as welded units with stems made of carbon structural steel, as assembled units with detachable cutters made of hard alloy, and as attachable units with welded hard alloy plates.