Adjustment screws are produced with what appears to be shaped like a volcano and the circular edge will, indeed, destroy the original flat upper edge of your fin. Such destruction leaves a roughness which prohibits easy tail adjustments. Avoid this by grinding down the volcanos using a nut to maintain a square end of the adjusting screw. If done properly a true square end of the adjusting screw will move the fin evenly and without ragging the fin edge.