Heat treated tool steel countersink with a HSS drill.
Adjustable for different length screws and can produce a counterbored hole for woodplugs.
The drill produces pilot holes only.

Specification:
D=1/2 inch
D=12.7 mm
D2=1/8 inch
D2=3.25 mm
Shank Diameter=1/4 inch hex
Softwood=No.10
Hardwood=No.8