Patent ID: 8490714

Claim:
An impact wrench comprising: a columnar spindle that can be rotated by a motor; an anvil that is disposed forward in a direction of a rotational axis of the spindle and whose rotational axis is coincident with said axis of the spindle, the anvil including, at a front portion thereof, a square shank portion to which a tightening socket can be mounted or a hole into which a driver bit can be inserted, and including a first claw at a rear portion thereof; a primary hammer that can be fitted to an outer circumference of the spindle and that includes, at a front portion thereof, a second claw for engagement with the first claw, the primary hammer being capable of rotating about the rotational axis of the spindle and of moving in the direction of said axis; a secondary hammer including a cylindrical portion that rotates integrally with the primary hammer, the cylindrical portion having an internal space into which the spindle can be inserted and in which the primary hammer can be housed; a rotary impact mechanism that is interposed between the spindle and the primary hammer, that causes, when a torque greater than a predetermined value is exerted between the spindle and the primary hammer, the primary hammer to rotate and advance in a direction of the anvil, and that strikes the first claw by engaging impulsively the second claw with the first claw, thereby causing the anvil to rotate about an axis; a center holding means that holds the rotational axis of the secondary hammer in coincidence with the rotational axis of the spindle; and a case that houses at least the spindle, the anvil, the primary hammer, and the secondary hammer, and that has an opening from which the front portion of the anvil projects, wherein the spindle and the secondary hammer are rotatably supported on the case via a first bearing and a second bearing, respectively, in a state in which axes of the spindle and the secondary hammer are coincident so that the case functions as the center holding means, and wherein the first bearing and the second bearing are attached to an inner circumferential face of a cylindrical bush and the bush is fixed to the case.