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 HelpOnEditing.
Example
--- (not a rule) ---- ----- ------ ------- -------- --------- ---------- -------------------------------------------- (not thicker than 10)
Display
--- (not a rule)
(not thicker than 10)