The size of the plaque should be convenient for use on active or inactive wells, e.g., a 17-centimeter (7-inch) square and 3 mm (1/8 inch) thick. Letter size of the word "CAUTION" should be approximately twice the letter size of the rest of the information, e.g., 12-millimeter (1/2-inch) and 6-millimeter (1/4-inch) letter size, respectively. Quantities and distances may be expressed either in SI units or in special and English units or in dual units.
Ill. Admin. Code tit. 32, pt. 351, subpt. E, app B