Counterbore with a slow spiral drill fitted.
Tungsten Carbide Tipped for use in abrasive materials.
Dimensions:
D=3/16 inch
D=4.75 mm
D2=1/2 inch
D2=12.7 mm
Shank Diameter=1/4 inch inch
Shank Diameter: 1/4 inch
Diameter Imperial: 3/16
Diameter Metric: 4.76
Diameter 2 Metric: 12.7