Properly join two pieces of wood by drilling a pilot hole, clearance hole and countersink or counterbore in one step! ACB (Adjustable Clearance Bore) countersinks have an integrated clearance bore cutter (blade). The depth of the clearance bore can be adjusted to match the thickness of your top board being fastened, allowing the screw to pass through, preventing separation and shifting during assembly. The clearance bore is adjustable for a 1/2", 3/4", 4/4" thick stock, but can also be used in 1-1/2 thick lumber if counterboring into the workpiece. Countersink body and boring blade are made from thru-hardened alloy steel for long cutting life.