9 CFR 2.51 - Form of official tag.
(a) The official tag shall be made of a durable alloy such as brass, bronze, or steel, or of a durable plastic. Aluminum of a sufficient thickness to assure the tag is durable and legible may also be used. The tag shall be one of the following shapes:
(1) Circular in shape and not less than 1 1/4 inches in diameter, or
(2) Oblong and flat in shape, not less than 2 inches by 3/4 inch and riveted to an acceptable collar.
(b) Each tag shall have the following information embossed or stamped on so that it is easily readable:
(1) The letters “USDA”;
(3) Numbers identifying the animal (e.g., 82488).