The 500 Series Rear-loading horizontal mailboxes are designed for use in larger multi-family apartment buildings, dormitories, office buildings, etc. The are recessed-mount boxes, and recess 17" into the wall. These lockable mailbox units can accommodate either U.S. Postal Service or private party access. The included lock type is a 5-pin tumbler lock with 1,000 key changes, two keys, and a clear plastic name/number slot for identification by tenants. Features all Aluminum construction. PLEASE NOTE: THESE UNITS ARE NOT USPS-APPROVED FOR NEW CONSTRUCTION. RENOVATION ONLY. Door sizes can be customized for double-wide, double-tall, or extra large. Please call for a quote on customized units. Standard door size is 5"H x 6-3/8"W. THis unit features 21 doors (3 Doors Wide x 7 Doors High) and is REAR-LOADING. Silver Color.