The in ground steel mounting post is made of heavy-duty 10-gauge to 14-gauge galvanized steel, with a durable powder-coated finish. The in ground post should be buried approximately 12" in ground, in order for the incoming mail slot mailbox to be within USPS (United States Postal Service) specifications of 41" to 45" above the roadside surface. This post will fit securely over a 4x4 wooden post for deep installations and reinforcement with rebar. Includes 4 mounting bolts and clear instructions. Limited lifetime warranty. Dimensions: 43" H x 4" W x 4" D. Black.