Simpson Strong-Tie connectors make projects easier to build while making them stronger and safer, engineered and tested to perform and manufactured to the highest quality standards. HDU holdowns are pre-deflected during the manufacturing process, virtually eliminating deflection under load due to material stretch. They use Simpson Strong-Tie Strong-Drive® SDS Heavy-Duty Connector screws (included), which install easily, reduce fastener slip and provide a greater net section when compared to bolts. HDU 13-3/16 in. Galvanized Predeflected Holdown with Strong-Drive® SDS Screws (Pack of 15).