Use these durable pedestals with either the 16 or 13 door CBUs to create a free-standing unit. Like the high-security cluster mailbox units, these pedestals feature a sturdy construction to provide years of use. CBUs are the primary freestanding, external delivery system for the USPS. Constructed of stainless steel, aluminum, and corrosion resistant-components, the CBU is approved for use throughout the U.S. in all weather conditions. The new F Spec CBUs are designed to meet or exceed the latest USPS standards, developed to increase the security of horizontal, high security CBUs to provide the safest personal mail delivery possible. Sandstone Color.