I use emery cloth. I typically will go with 120 grit then 180 grit and finish off with 220 grit. It just depends how bad the joint/scratches are. I take a 16" - 18" piece and sand back and forth right to left. Some real bad joints need to have a fine file taken to them first then a 60 or 80 grit then finished with the finer grit. I've seen some bad piston joints on larger jacks that have had to be filed.