After match drilling with #40 I debur all the holes both sides. I also debur the skin edge with the debur tool and sand paper. Then I dimple the stiffeners on the DRDT-2. I also dimple the skin on it. Then I take two turns with the countersink tool off the stiffener holes to accept the skin dimple. Just seems to me the receiving dimple has to be slightly larger than the skin dimple. Two turns with the countersink tool isn't much.