【Countersink Bits】Steel countersink bits are used for drilling holes in wood or other hardwood floors and are suitable for bench drills, hammer drills, chuck drills, etc. It is a must-have item for daily woodworking.【Drill Bit Set】4pcs HSS constructed drill bits for drilling holes with screw sizes 5#, #6, #8, #10 and #12.【Special Design】Special designed steel bushing countersinks or counterbore hole【Fast Chip Ventilation】The hex countersink drill bits features a chip flute and a three-sided chamfering machine that quickly discharges wood chips to achieve a smooth surface on any type of hardwood.【Easy to Use】Adjustable sleeve depth with hex wrench, the drilling length can be adjusted for different length screws simply by loosening and tightening the set screw. These tools complete pilot holes and countersinking for screw head housing in one operation. Delivery in a wooden box.Safety:The drill bits should be used on a drill.The rotation speed of the machine should be between 1200 and