Two 3/8" copper, two brass, and one silver or nickel silver discs need to be domed to fit inside the cut hole in the washer. My discs were domed to fit a well that my #12 dap fit. Pass the domed disc across 400 grit sandpaper on a bench block several times to create a somewhat flat bottom edge. Under normal circumstances, there would be a worry that the expanding air inside the disc could "blow the disc off the link" during soldering. However, the link is textured and not perfectly flat, so this is not going to be a problem as air can escape where the pieces do not fit together perfectly.