Keys and other small articles

§ 4651. Keys and other small articles (a) Any person may mail without prepayment of postage a key, identification card, identification tag, or similar identification device, or small article which the Postmaster General by regulation designates, which bears, contains, or has attached securely thereto— (1) a complete, definite, and legible post office address, including any street address or box or route number; and (2) a notice directing that it be returned to the address, and guaranteeing the payment, on delivery, of the postage due thereon. (b) Postage at the rate of 5 cents for each two ounces or fraction thereof shall be collected on delivery.