Antique U.S. Post Office mailbox door, typically made of bronze and featuring a "Flying Eagle" or sunburst design. 
Key Features
• Design: These doors often depict an eagle with outstretched wings set against a sunburst pattern.
• Mechanism: It features a single-dial combination lock at the top.
• Dimensions: Common sizes for these salvaged doors are approximately 3 5/8" × 6"
• Material: Most are crafted from solid brass or cast bronze. 

 I do NOT know the combination to the lock.