Combination countersink and/or counter bore for standard wood plugs. The counter bore size is 3/8" for use on hard or soft wood. Standard hex shank fits all power bit quick change chucks. Alloy steel & 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 & clean chip removal. Made in USA by Snappy.