Abstract: A power wrench includes a relatively flat elongated housing with an output shaft at one end operatively connected to one end of a drive segment lever arm whose opposite end is connected to a hydraulic cylinder mounted transverse to the lever arm. The hydraulic cylinder is connected through hydraulic lines to an external reservoir which is subject to variable hydraulic pressures through a power source. A valve alternately admits hydraulic fluid to opposite ends of the cylinder causing the cylinder to reciprocate which in turn oscillates the aforementioned opposite end of the lever arm to unidirectionally rotate the output shaft.