Black Silicone Rubber Caulk Sealant. Use to seal rails, corners, seams, and fasteners in battery containment systems. Conforms to ASTM spec C920, class 25 Grade NS. Minimal shrinkage, 50-year life. Use to seal rails, corners, seams, and fasteners. Conforms to ASTM spec C920, class 25. grade NS Clear color, minimal shrinkage, 50-year life.