Impact wrenches are wrenches that are able to deliver high output of torque. These wrenches first store energy in a rotating mass, and then deliver it in a sudden action to the output shaft. Impact wrench, is a tool you use when no other wrench is working. For example sometimes lug nuts are too tight in their place or head of the screws may be too stripped and a regular wrench can't get a grip. Impact wrench allows the user to torque the screw easily and with minimum effort in this situations. An impact wrench has a motor which works with electricity or air (there are cordless models as well) and applies a sudden, intense twisting motion to the lug nut that is recalcitrant.