Em dash vs. En dash
express strong grammatical breaks. An em dash is one em wide—the width of the point size of the typeface. In manuscripts, dashes are often represented with a double hyphen (–); these must be replaced.
— em dash = shift-option-hyphen
serve primarily to connect numbers (1–10). An en is half the width of an em. Manuscripts rarely employ en dashes, so the designer needs to supply them.
– en dash = option-hyphen