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=1/4 inch Plug size=6.3 mm Taper range approx.=6.3 to 6.6 mm Shank Diameter: 1/4 hex Diameter Imperial: 1/4 Diameter Metric: 6.3