Dash/rule: En dash (BrE: En rule) –, and Em dash (BrE: En rule) —

a.   Use an en dash (not a hyphen) to indicate inclusive or continuing numbers, as in dates, page references or Scripture references.

e.g.     pp. 23–46

                  1970–73

                  January–May 1994

                  Acts 2:35–40

b.   Use an em dash (—)  to separate a string of words. Used either in pairs, or singly. Use sparingly.

i.     In pairs they mark off a parenthesis in the middle of a sentence. Some British authorities use a spaced en dash in this situation, but not all. Hence Japan Harvest will use an unspaced em dash.

e.g. After that—and in concert with that—he wants peace and prosperity for Rome.

ii.     A single em dash is used like a colon.

e.g. A display of aggression quite wasted on Pompey—which Milo knew, but did from force of habit.

iii.     Used to denote an abrupt break in thought that affects sentence structure.

e.g. “He hasn’t marched? He—which legion?”

c.    Use a 2-em dash (no space on either side) to indicate missing letters in a word.

e.g.     Melody P——k voted no.

d.   Use a 3-em dash (with space on each side) to indicate that a whole word has been omitted.  In British style, a spaced two-em is used in this situation.

e.g.     The ship left ——— in May.

e.   Note: an en dash is longer than the hyphen that you find on most keyboards. On Mac OS, an en dash is easily created using Option-hyphen; an em dash by using Option-Shift-hyphen. On Microsoft Word’s default settings, in both Windows and Macintosh versions, an em dash symbol, which is not always a true em dash from the font, is automatically produced by Autocorrect when two unspaced hyphens are entered between words (“word–word”). An en dash, which again is not always a true en dash from the font, is automatically produced when one or two hyphens surrounded by spaces are entered: (“word — word”) or (“word — word”)