Counterbore with a slow spiral drill fitted.
Tungsten Carbide Tipped for use in abrasive materials.
Dimensions:
D=1/4 inch
D=6.35 mm
D2=5/8 inch
D2=16 mm
Shank Diameter=1/4 inch hex
Shank Diameter: 1/4 hex
Diameter Imperial: 1/4
Diameter Metric: 6.35
Diameter 2 Metric: 16