Hinge #1, 14 gauge steel, black powder coated finish. The #1 goes between the bottom section and the second section up. That's where the least roller offset is needed because the door is still close to vertical at that point. The powder coat gives it better corrosion resistance and a cleaner look than bare steel. If your existing #1 hinge is cracked, bent, or rusted, just match the number stamped on the old one. Using the wrong hinge number in the wrong position puts the roller in the wrong spot and the door won't track right.