Fit the base into the 3½-inch gaps in the legs so that the ends are flush with the outer edges of the legs. Check the base for level, from front to back and side to side, and make adjustments as necessary. Secure the base by driving 2⅝-inch screws through the front and back of the base and into the inside faces of the legs. Cut all 2x4 crosspieces to size, and fit the lower ones into the gaps in the legs beneath the base. Secure them by toenailing 3-inch screws through the crosspieces and into the inside faces of the legs. Secure the legs to the post anchors with the supplied lag screws, adding shims if necessary.