An Impact Wrenches (also called air wrench, air gun, torque gun) is a powered socket wrench that provides high-torque output with minimal exertion required of the user. The tool's power source is compressed air or hydraulics or electricity (via cord or battery). Impact wrenches are available in various socket drive sizes-from 1/4 inch (for small assembly/disassembly) to 31/2 inches (for major construction), which is a major determinant of price.