These combination units are specifically designed for woodworkers. The high-speed tapered drill bits are precisely ground on a CNC grinder and match the shapes of wood screws so that screw threads grip for the entire length of the screw. Our countersink/counterdrill units (unlike most others) are hardened; they are also sharpened after hardening. Used in combination with a stop collar, they let you set the unit for a wide range of screw lengths for everything from flush countersinking to a full 1/2" of counterdrill. The drills are multi-purpose and will serve the needs of most woodworkers for both hard and soft woods. 2 3/4" to 4" long overall. For softwood, you should always use a drill one size smaller than the screw calls for.