An impact wrench is a socket wrench power tool designed to deliver high torque output with minimal exertion by the user, by storing energy in a rotating mass, then delivering it suddenly to the output shaft. In operation, a rotating mass is accelerated by the motor, storing energy, then suddenly connected to the output shaft (the anvil), creating a high-torque impact.
Compressed air is the most common power source, although electric or hydraulic power is also used, with cordless electric devices becoming increasingly popular since the mid-2000s.
