Combination countersink and/or counter bore for standard wood plugs with standard hex shank will fit all power bit quick change chucks. Made of alloy steel & thru hardened with a 82 degree countersink angle. The drill bits are adjustable for different length screws with a 3/8" or 1/2" diameter counter bore. Your drill will not slip when using large 1/4" socket head screws. Made in USA by Snappy.