Our 3/16" steel mailbox adapter plates allow you to install multiple mailboxes on one post (choose from our 2-box, 3-box, or 4-box plate). These adapter plates work with our standard Northwest boxes (Columbia, Gorge, or Cascade) and our Universal in-ground or surface post. Powder coated in different colors to match mailboxes and posts (Black, White, Stone, Pearl Taupe, Mallard or Juniper Green).