There are two (common) dash characters wider than a hyphen, commonly called an "em dash" and "en dash". (So called because they're approximately the width of a capital M and a lower-case N respectively). Some style guides don't approve of em dashes much at all, but in those that do use both there are clear rules on when to use an em and when an en. The Wikipedia "dash" article describes some such rules:
The em dash (—), or m dash, m-rule, etc., often demarcates a parenthetical thought or some similar interpolation, such as the following from Nicholson Baker's The Mezzanine:
At that age I once stabbed my best friend, Fred, with a pair of pinking shears in the base of the neck, enraged because he had been given the comprehensive sixty-four-crayon Crayola box — including the gold and silver crayons — and would not let me look closely at the box to see how Crayola had stabilized the built-in crayon sharpener under the tiers of crayons.
The en dash is commonly used to indicate a closed range (a range with clearly defined and non-infinite upper and lower boundaries) of values, such as those between dates, times, or numbers.
Some examples of this usage:
- June–July 1967
- 1:00–2:00 p.m.
- For ages 3–5
- pp. 38–55
- President Jimmy Carter (1977–1981)
But typing a sentence such as the following into a Microsoft office application: "The game -- suitable for ages 3--10 -- could hardly have been expected to hold our attention" autocorrects to "The game – suitable for ages 3—10 – could hardly have been expected to hold our attention". Exactly the opposite of what we would expect.
This does my head in.