Architectural Mailboxes 950020B-10 Centennial Postmount Mailbox, XL, Black Larger inner compartment can accept a USPS priority mail large flat rate box 12 in. x 12 in. x 5.5 in. and still has room for additional mail and parcels Heavy gauge galvanized steel body equipped with stainless steel door pins then fully powder coated for corrosion resistance Sleek magnetic door closure provides reliability all while keeping door firmly closed Predrilled 4 in. x 10 in. hole pattern in floor allows for mounting to existing post installation hardware not included Order Architectural Mailboxes adapter plate 7540B for 4 x 4 wood post installation