Under 49 CFR Part 172.325, HOT markings are required for bulk packaging that contains an elevated temperature material (except molten sulfur or molten aluminum). You can use markings printed with HOT and or 3257 to satisfy both the 4-digit number and HOT marking requirements of 49 CFR, Part 172.325(c) and 172.336(b). Heavy-duty Spacemaster frame is constructed of corrosion-resistant, fully formed aluminum alloy. DOT placard panels are made of aluminum alloy 3105-H16 and mill roller coated with white acrylic paint. 4 double-riveted stainless steel fasteners hold the panels securely in place. Flip Placard System for Trailers printed with HOT and 3257 is sold per each.