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® screws (SDS) which install easily and provide reduced fastener slip. Using SDS screws results in a greater net section, when compared to bolts, as no material is removed. The HDU series of holdowns are designed to replace previous versions of the product such as PHD’s as well as bolted holdowns. The HDU2, 4 and 5 are direct replacements for the PHD2, 5 and 6, respectively. For more information on holdown options, contact Simpson Strong-Tie. HDU Special Features: Pre-deflected body virtually eliminates deflection due to material stretch. Uses SDS screws which install easily, reduces fastener slip, and provides a greater net section area of the post compared to bolts. SDS screws are supplied with the holdowns to ensure proper fasteners are used. No stud bolts to countersink at openings. Material: See table. Finish: HDU—Galvanized Installation: Use all specified fasteners. See General Notes. For use in vertical and horizontal applications. The HDU requires no additional washer, the DTT requires a standard cut washer (included) be installed between the nut and the seat. To tie multiple 2x members together, the Designer must determine the fasteners required to join the members to act as one unit without splitting the wood. See SDS Screw information. See SB and SSTB Anchor Bolts for anchorage options. SDS screws install best with a low-speed, high-torque drill with a 3/8″ hex head driver. Refer to Anchor Designer Software™ for ACI 318 for anchoring solutions.