nines
n.— «One proposal is to require that the most dangerous substances be burned 99.9999 percent—the “six nines,” the company calls it.» —“U.S. urged to hurry waste disposal plans” by William E. Clayton Jr. Houston Chronicle (Texas) Apr. 11, 1985. (source: Double-Tongued Dictionary)
Further reading
While reading Great Expectations (Bookshop|Amazon) by Charles Dickens, a listener in Arlington, Texas, is surprised when one of the characters inherits some money, which Dickens describes as a cool four thousand. Were they really using cool that way...