This tool works like a charm! I made it so I could remove the stock lens from my GoPro Hero4 Black without damaging the lens. Now I can install an aftermarket lens that doesn't have the fish-eye distortion. I can keep the old lens as a backup, or sell it. Will probably work also with other GoPro cameras and various sport cameras with a 18mm diameter lens. I made the tool extra large to make sure it would work. I printed it with a thick wall (5 perimeters), but only 20% infill.