Tool (or bit) used with a carpenter's brace for drilling holes, usually in wood.
It looks like a corkscrew and produces extremely clean holes, almost regardless of how large the bit is. Expansive auger bits have adjustable blades with cutting edges and spurs that can be extended radially to cut large holes. Large augers are used to bore holes in soil for fence posts and telephone poles, or in ice for ice fishing. Horizontal augers as much as 8 ft (2.5 m) in diameter are used in coal mining.