Combination countersink and/or counter bore for standard wood plugs. The counter bore size is 3/8" for use on soft wood using a # 6 screw. Standard hex shank fits all power bit quick change chucks. Alloy steel and thru hardened for long life - can be resharpened. Your drill will not slip when using large 1/4" socket head screws. Two flute construction for fast and clean chip removal. Made in USA by Snappy.