23. A quick pass using a dual-action sander reveals whether the low and high spots have truly been removed. Similar in method to how the body file was used earlier, the DA skims over the surface, revealing any low and high spots. Very minor surface irregularities can also be removed as the sander passes over the area, though care must be taken to avoid making the surface too thin. With the dents removed, the rest of the fender can be blocked out and prepped for paint.