Simpson Strong-Tie HDU Holdowns are pre-deflected to virtually eliminate deflection under load due to material stretch. The Strong-Tie HDU8-SDS2.5 pre-deflected holdown is installed with Simpson Strong-Drive SDS heavy duty connector screws which are included with the holdown. HDU Special Features Holdown designs virtually eliminate deflection due to material strech. Uses Strong-Drive SDS Heavy-Duty Connector screws which install easily, reduce fastener slip, and provide a greater net section area of the post compared to bolts. Strong-Drive SDS Heavy-Duty Connector screws are supplied with the holdowns to ensure proper fasteners are used. No stud bolts to countersink at openings. Installation: Use all specified fasteners. The HDU requires no additional washer, the DTT requires a standard cut washer (included with DTT2Z) be installed between the nut and the seat. Strong-Drive SDS Heavy-Duty Connector screws install best with a low speed high torque drill with a 3/8" hex head driver. NOTE: The correct fasteners installed in the correct position must be used to achieve published load values California Residents: WARNING