An Atlantic crossword clue baffles

In today’s Atlantic mini-crossword, 5-A, three letters, “11-character fig. on a form.” The answer, of course, is SSN. But a Social Security number has nine digits.¹ And why does the clue read characters ? Am I missing something?

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Elaine, who does not do crosswords, just explained it to me: nine digits and two hyphens: eleven characters. Sneaky, sneaky clue. Good thing I'm married.

            
¹ Nine digits, unless you’re Ralph Kramden, whose number has only seven.