Abstract: An improvement to a conventional slap-hammer which allows the hammer to be rotated by a pneumatic wrench or like device. A universal joint is attached to the top of the slap hammer to enable the latter to be rotated by the output shaft of a pneumatic wrench. The housing of the wrench is held by a closable harness that encircles the housing when closed and thereby prevents the output shaft from becoming disengaged from the universal joint.