16 CFR 500.17 - Fractions.
(a) SI metric declarations of net quantity of contents of any consumer commodity may contain only decimal fractions. Other declarations of net quantity of contents may contain common or decimal fractions. A common fraction shall be in terms of halves, quarters, eighths, sixteenths, or thirty-seconds; except that:
(1) If there exists a firmly established general consumer usage and trade custom of employing different common fractions in the net quantity declaration of a particular commodity, they may be employed, and
(2) If linear measurements are required in terms of yards or feet, common fractions may be in terms of thirds. A common fraction shall be reduced to its lowest terms; a decimal fraction shall not be carried out to more than three places.
(b) If a statement includes small fractions, smaller variations in the actual size or weight of the commodity will be permitted as provided in § 500.25, than in cases where the larger fractions or whole numbers are used.