For flat cables, such as Ancor #6, make two measurements. The thickness and the width. Drill two holes, whose outside circumferences are slightly larger than the cable sheath width, and whose diameter is slightly larger than the thickness of the cable sheath. Make a razor cut through the rubber seal that passes from the outside, through one hole and into the second hole. With the razor, trim the two triangles of rubber that separate the two holes (open up the rubber seal and lay it out flat to facilitate the trimming). Now assemble the Cable Clam with the flat cable and you have a water-tight seal. The picture shows two separate cables, but the principle is the same.