4" Diameter 47" long round post is 14 ga. steel, designed to be put into freshly poured cement. (Surface mounting not available.) The mailbox secures to its post (included) with a special secure locking collar. No screws, bolts or seams are visible, making it almost impossible for even skilled professional criminals to penetrate the Secure Mail Vault™. New, more robust keyless entry (keypad) means no keys to carry and easy entry. Dual-door system for maximum protection - outer door closes solidly with a rare-earth magnet. Outgoing mail is placed in the outgoing mail clip inside the outer door, ready for the letter carrier to pick up. Accepts parcels up to 1¾" thick through 10½" x 2¾" incoming mail slot. There's a red outgoing-mail flag that you can just see in the photo of the open mailbox. It's at the lower right edge of the mailbox - pulls straight out to notify the letter carrier.
Dimensions:
Overall: 12 3/8" wide x 18" high
x 21" deep
Outer Door: 10¾" x 7 5/8"
Keypad: 4¼" x 3 7/8"
Mail compartment: 10¾" x 8¼" x 18"
Incoming Mail Slot: 10½" x 2¾"