Architectural Mailboxes Universal Adapter Plate White This adapter plate is used when mounting any Architectural Mailboxes 5500 series mailbox to either a 5515 or 6215 post. The adapter is placed under the mailbox and attaches to directly to the support arm. This adapter plate is required when mounting any 5500 series mailbox to an Architectural Mailboxes spreader plate. Models include 5112 Duo Spreader, 5113 Triple Spreader, and 5114 Spreader. This adapter plate can be used when mounting a 5100 series mailbox or 5103 series Dropbox to a top mount 4x4 wood post. Zinc plated assembly bolts and nuts are included. Unit size is 9" x 5" x 1" and weighs 2lbs.