Counterbore with a slow spiral drill fitted.
Tungsten Carbide Tipped for use in abrasive materials.
Dimensions:
D=5/32 inch
D=4 mm
D2=3/8 inch
D2=9.5 mm
Shank Diameter=1/4 inch hex
Shank Diameter: 1/4 hex
Diameter Imperial: 5/32
Diameter Metric: 4
Diameter 2 Metric: 9.5