Horizontal Rules
You can insert a horizontal rule across the page by typing four or more dashes. The number of dashes in a horizontal rule markup determines how thick it is, up to a limit of 10.
For more information on the possible markup, see Help On Editing.
Example
--- (not a rule) ---- ----- ------ ------- -------- --------- ---------- -------------------------------------------- (not thicker than 10)
Display
— (not a rule)
——————————————— (not thicker than 10)