2.5mm diameter hex shank Counter Bit Set. 4 piece set includes bits set for drilling pilot holes for screw sizes #6, #10, #13,and #16. Standard 2.5mm Hex drill bits shank is quick change compatible. Function: can drill the screw holes and keep on the same axis, after screw in screw nut below the board! Function: can drill the screw holes and keep on the same axis, after screw in screw nut below the board! Special designed steel counter sleeve countersinks or counter bores pilot hole. Drilling length can be adjusted for various length screws simply by loosening and tightening the setscrew. Material: HSS - Christmas Gift for Dad/Father,Husband, Boyco.ukiend, Men,DIY Handyman. Apply to with a clamp or joint drilling machine, suitable for drilling in the hard wood and wood floor, machine screw for wood screw. Features: brand new and high quality,sharp and durable. 4pcs set includes bits for drilling pilot holes for screw sizes #6 #10 #13 #16 Including a mini hex wrench. It can drill the