Made from Tool Steel. Plugs are very slightly tapered. Recommended for use with a pillar drill. Use on timber to make plugs/pellets to plug screw holes Dimensions: Shank Diameter=1/4 inch hex Plug size=7/16 inch Plug size=11.1 mm Taper range approx.=11.1 to 11.4 mm Shank Diameter: 1/4 hex Diameter Imperial: 7/16 Diameter Metric: 11.1