To begin with, the posts are different between the m1-lt mailbox, the small standard mailbox, and all the other larger mailboxes. The only difference is the width of the post. (2.5″ x 2.5″ for the m1-lt mailbox, 4″ x 4″ for the small standard mailbox, and 5″ x 5″ for the larger mailboxes) mainly just for looks, but both offer the same strength. They are all made of the same 1/8″ steel square tubing. They then have a welded plate for mounting the fort knox mailbox which is then fastened with carriage bolts on top of the post.