What size and shape must a standard hazardous-materials placard have?
Correct answer: D – A square-on-point measuring at least 250 mm (9.84 inches) on each side
Federal hazardous-materials regulations require each standard diamond, or square-on-point, placard to measure at least 250 mm (9.84 inches) on each side. The Vermont CDL manual uses the same dimensions and shape. Package labels are smaller and should not be confused with vehicle placards.
Source: Vermont Commercial Driver’s License Manual — § 9.3.3, “Lists of Regulated Products”, 49 CFR § 172.519(c) – General specifications for placards

