Lightweight Concrete Base Sheet Fasteners twin legged, expanding base sheet fasteners. These are designed for the attachment of base sheets to lightweight, insulating concrete roof decks. These are manufactured from G-90 galvanized steel. These are coated with a corrosion-resistant coating. The head diameter is 1.1″ (28 mm) and the leg length is either 1.2″ (30 mm) or 1.7″ (43 mm).