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. For trim head screws. Dimensions: D=1/4 inch D=6.35 mm D2=1/8 inch D2=3.25 mm Shank Diameter=1/4 inch hex Screw size Trim head screw Softwood=No.10 Hardwood=No.8 Shank Diameter: 1/4 hex Diameter Imperial: 1/4 Diameter Metric: 6.35 Diameter 2 Metric: 3.2