4-Piece Countersink Drill Bit Sets Hex Shank Sets #6 #10 #13 #16 W/ Key (Silver) Material: HSS 4241 Four piece set includes bits for drilling pilot holes for screw sizes #6, #10, #13, #16 Special designed steel counter sleeve countersinks or counter bores pilot hole Standard hex shank is quick change compatible. Drill and countersink for wood screws without changing bits Apply to with a clamp or joint drilling machine, suitable for drilling in the hard wood and wood floor, machine screw for wood screw.