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=5/16 inch Plug size=7.9 mm Taper range approx.=7.9 to 8.2 mm Shank Diameter: 1/4 hex Diameter Imperial: 5/16 Diameter Metric: 7.9