Countersink Bits
From DT Online
Countersink Bits or drills, are used to Chamfer or bevel the edge of a drilled hole such that a Countersunk Head Screw can be seated flush with material surface.
They are available in a range of point angles but the most common for general purposes is 90°. Short fluted designs are chosen for working in metal and are made of High Speed Steel (HSS) for this purpose. The longer Rose Countersink is made of Carbon Steel but is often prefered for working in wood.