Simpson 20-5/16" Bolted Hold Down Anchor HD12The HD is designed to create high allowable loads for both vertical and horizontal applications in wood construction. This holdown is installed with bolts into posts or columns. The HD can be installed back to back when eccentricity is an issue. Model No. HD12 Base Seat Thickness (in.) 3 8 Ga. 3 SB (in.) 4 HB (in.) 7 W (in.) 3 1 2 H (in.) 20 5 16 B (in.) 4 1 4 CL (in.) 2 1 8 SO (in.) 3 5 8 Coating Material. Simpson Strong Tie Gray Paint Key Features