49 CFR § 172.527 - Background requirements for certain placards.
(a) Except for size and color, the square background required by § 172.510(a) for certain placards on rail cars, and § 172.507 for placards on motor vehicles containing a package of highway route controlled quantity radioactive materials, must be as follows:
(b) In addition to meeting the requirements of § 172.519 for minimum durability and strength, the square background must consist of a white square measuring 14 1/4 inches (362.0 mm.) on each side surrounded by a black border extending to 15 1/4 inches (387.0 mm.) on each side.
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