Salsbury Industries 4370WHT Deluxe Post 1 Sided In-Ground Mounted for Roadside Mailbox, White 1-sided deluxe mailbox posts include a 15-1/2" W x 3-1/2" D x 3-1/2" H arm 2-sided deluxe mailbox posts for two mailboxes include two 15-1/2" W x 3-1/2" D x 3-1/2" H arms 2-sided deluxe mailbox posts for three mailboxes include one 15-1/2" W x 3-1/2" D x 3-1/2" H arm and one 27-1/2" W x 3-1/2"D x 3-1/2" H arm 2-sided deluxe mailbox posts for four mailboxes include two 29" W x 3-1/2" D x 3-1/2" H arms Minor assembly is required. Salsbury Industries is an ISO 9001: 2008 certified company and has excelled in the field of manufacturing since 1936