Flexible 36-grit discs were used on the drivers side panel. And these made all the difference. I didn't use as much pressure when grinding the welds down and only for about 30-seconds at a time, then cooled the metal off with compressed air. I'm not a patient person by nature so taking that much time to weld then grind nearly killed me. But, I can tell you that the metal warping on the driver's side is negligible and will require minor hammer and dolly work just for good measure.