Combination countersink and/or counter bore for standard wood plugs. Thecounter bore size is 3/8" for use on hard or soft wood using a 8 screw onhard wood or 10 screw on soft wood. Standard hex shank fits all power bitquick change chucks. Alloy steel & thru hardened for long life - can beresharpened. Your drill will not slip when using large 1/4" socket headscrews. Two flute construction for fast & clean chip removal. Made in USA bySnappy.