Strong Line is a thin coppered steel strip used to strengthen your stained glass panel from the inside. The coppered steel strip is just the right size for your copper foil or lead came projects. Why use Strong Line Most people use it to eliminate external bars. How much can be eliminated is a tough question because it depends on the size, design and intended istallation of your panel. Remember to error on the side of stronger. 25 feet long by 0.20 inches thick by .114 inches wide.