US Patent 7255029 Manually operated impact tool

A manually operated impact tool having: a handle; an anvil movably connected to the handle, the anvil having an anvil surface, the anvil further having a fastener engagement portion for engaging a fastener to be loosened or tightened, the fastener engagement portion being substantially rigidly attached to the anvil; a hammer movable with respect to the anvil and handle, the hammer having a hammer surface in cooperation with the anvil surface; an energy storage device for storing potential energy upon a relative movement of the handle and hammer; a locking device for preventing relative movement between the hammer and anvil during the relative movement of the handle and hammer; and a locking release device for unlocking the locking device upon an amount of the relative movement of the handle and hammer such that the potential energy stored in the energy storage device is at least partially transferred to the hammer such that the hammer surface contacts and impacts the anvil surface and at least part of such impact is transferred to the fastener through the fastener engagement portion.