The mandrel is attached to a thin shaft with a small, straight-head screw on the end. First, remove the screw and the red washer, located behind the screw, with the combination wrench/screwdriver included in the kit or a regular screwdriver. Place one of the cut-off disc on the mandrel, with the washer on top of the disc. Insert the screw into the round opening in the disc and tighten. Now, you are ready to attach to the mandrel to the tool.