Combination Drills - Counter Sinks
This convenient tool combines the drilling and countersinking of a hole in one operation. The advantage is assurance of alignment of both sections of the process.
The plain type combination drill & countersink produces a seat or bearing surface for subsequent machining operations. It's the most commonly used and produces a 60 degree angle satisfactory for turning or grinding.
These “radius” combination drills and countersinks are designed to reduce the bearing surface of the center hole and provide a protected centering seat while reducing the risk of breakage.