Can this be slid over metal post already in ground ?

Hello, although the post will be able to slide over another post that is smaller than 3" in diameter, the Hamilton Black Mailbox Post is designed to be installed into the ground. Sliding the Hamilton Post over an existing post may not meet USPS height requirements. Thanks for reaching out! Should you have further questions, don't hesitate to contact us directly at support@architecturalmailboxes.com.