Abstract: The invention is a tool 50 for a clamp assembly used to secure wire harnesses 12 and the like to appropriate structure 14. The clamp is of the type having apertured end members 22 and 24 which are secured by means of a screw 34 and nut 46 assembly which extend through the apertures. The tool 50 comprises a guide member 52 having first and second ends with a pair of legs 56A and 56B extending from the first end in a spaced relationship. The spacing of the ends is slightly greater than the width of the ends of the clamp. The guide member 52 further incorporates an aperture 60 therethrough exiting the first end between the legs. A drive member 66 is rotatably mounted in the aperture 60 and incorporates a socket 76 facing the first end which is adapted to contain and drive the nut 46. A retaining assembly 70 and 74 is provided which is adapted to prevent the drive member from withdrawing from the aperture.