Add security to your post mount Lewiston Mailbox System with a locking insert that mounts inside your E1 Economy mailbox. Locking insert is made of galvanized steel and features a tough powder coat finish keeping mail secure from unwanted hands. Incoming mail slot opening: W 6 3/8" x H 1". Locking door opening: H 5" x W 6 3/8". A lock and keys are included.