The 20 Door Rear Loading Mailboxes are built from USPS specifications and are commonly seen in post offices across the country. Two units form one column in your wall or Rotary Enclosure. The P.O. boxes are designed to stack two high and mount next to each other between wall studs. These private P.O. boxes are great for universities, postal centers, military bases, mailrooms, and hospitals. Units are REAR-LOADING and must be mounted in-wall or in a rotary enclosure. Each door measures 5.5"W x 5.5"H and features a lock with two keys. Units featuring combination locks are available - Please call for quote.