We’ve been at this for a long time and we’ve seen almost every kind of installation under the sun. The majority of installations use a 4×4 wooden post, and we have a great solution for it: the 3-way 4×4 adapter plate. If you have a post made by one of our competitors, our mailbox will fit it if it uses the informal industry standard 4″ x 10″ bolt pattern. Here is an illustration of our bolt pattern, and every one of our post mount mailboxes uses this pattern. If your existing post uses a different pattern, we recommend attaching your own “DIY” wooden adapter to your existing post, then attaching your mailbox using the 4″x10″ pattern. Do not drill new holes into your mailbox or it will promote corrosion and void your warranty.