This set incorporates two drill countersinks and matching plug cutters.
Plugs cutters are made from Tool Steel and are very slightly tapered.
Use on timber to drill a countersunk hole for a screw which is then plugged uses a plug/pellet made using the plug cutter.
Recommended that plug cutters are used in a pillar drill.

Specification:
D=3/8 inch
D=9.5 mm
D2=7/64 inch
D2=2.75 mm
No.10 drill/countersink
D=1/2 inch
D=12.7 mm
D2=1/8 inch
D2=3.2 mm
Shank Diameter=1/4 inch hex
Screw size=No.8
Screw size=No.10

Includes:
1 x Drill/countersink for No. 8 x 9.5mm
1 x Drill/Countersink for No. 10 x 12.7mm
1 x Plug cutter 9.5mm (3/8 inch)
1 x Plug cutter 12.7mm (1/2 inch)