Make it Snappy Tools ACB Countersink performs 3 steps in one operation. 1. Drill a Pilot Hole - Allows your wood screw to engage just the right amount of material to avoid splitting and cracking 2. Cut a clearance hole in the top board - A clearance hole is large enough for the screw to pass through the top board without the threads engaging it, preventing separation and shifting during assembly. 3. Countersink or Counterbore - Countersink into the top board to allow the head of the screw to sit flush with the surface of the board. Or counterbore farther to set the screw below the surface allowing you to plug the hole. The pilot drill and clearance bore are both adjustable to accommodate different material sizes.