I faced a challenge: I couldn’t attach all of the 4×4 railing posts directly to the deck’s substructure, so I’d have to mount some onto the deck surface—usually a recipe for a wobbly railing. Post anchor kits from Titan gave me a solid, code-compliant solution.
Assembly is simple: bore a 1/4″-dia. hole—as straight as possible—in the base of the 4×4, and insert the anchor’s stem. Hammer the stem home; its sharp rim will wedge into the wood for a solid connection.
Secure the kit’s plate to the post with four galvanized lag screws. If the decking is 5/4 boards, double them from below to give the screws enough purchase, then screw the plate to the deck surface with eight heavy-duty 1⁄4″-dia. screws. You’ll probably need plastic shims to plumb the post.
The 4×4 anchors are $19 at Lee Valley. You can also buy hardware kits and anchors for 6×6 posts.