Abstract: A split roller block assembly is interposed and captively retained between facing surfaces of the drive pin and drive piston rod disposed within the housing of a hydraulic power wrench. The assembly smoothly couples these two elements to substantially strengthen the interconnection therebetween to increase the useful life of the wrench. The wrench is additionally provided with a reaction arm portion which is removably connectable to the wrench housing in a multiplicity of rotational orientations relative thereto, the reaction arm being rotationally locked to the housing in each such orientation. Reverse rotation of the drive shaft portion of the wrench is precluded by a safety pawl and ratchet system mounted externally on the wrench housing.