US Patent 7918286 Impact tool

In an impact tool including a spindle, an anvil, and an impact mechanism having a hammer and a coil spring, a restricting portion is provided at a front surface of a large-diameter portion of the spindle so as to receive a rear end of the coil spring and to restrict an inner diameter of the rear end of the coil spring. A ring-shaped groove is formed at a rear surface of the hammer to receive a front end of the coil spring, in a manner which provides an inner cylindrical portion at a rear side of the hammer. A run-off portion is formed in the restricting portion so as to allow the inner cylindrical portion of the hammer to move thereinto, so that the hammer can move backward for a distance corresponding to a depth of the run-off portion.