In order to ensure your screws sit flush, a countersink can be used. This Ryobi countersink set includes 4 different sizes for different jobs. Included is #6, #8,#10, #12. Each countersink is combined with an adjustable length pilot bit to help ease the process. This will eliminate having to guess which size pilot bit to use before creating the borehole. Use the included allen key to make the adjustments. Once the borehole is made, you are ready to apply your fasteners. Use this Ryobi Countersink Combination Set to help make your job easier.