2.14.3 Freight-Car Enclosure
Above the 1825 mm (72 in.) level, the walls and top of the enclosure shall be metal with or without perforations, except that portion of the enclosure wall in front of and extending 150 mm (6 in.) on each side of the counterweight, which shall be without perforations.
Perforated portions of enclosures shall reject a ball 25 mm (1 in.) in diameter.