Story highlights Trump trails Clinton by only two points

Fox polls will be used to help determine whether third-party candidates make the debate

Washington (CNN) Hillary Clinton is clinging to just a two-point national lead over Donald Trump, according to a new poll, a far narrower margin than most other surveys show.

Fox News survey published Wednesday shows Clinton winning 41% of the vote to Trump's 39%, with third-party candidates Gary Johnson and Jill Stein earning 9% and 4% respectively.

That difference is not statistically significant, and it is a tighter spread than other recent national polls. Two other polls released this week -- by Monmouth and Quinnipiac Universities -- showed Clinton with 7-point leads.

In a two-way race without Johnson and Stein, Fox finds Clinton's lead extends to six points, 48% to 42%. That is narrower than the 10-point lead that Fox said Clinton had following the Democratic National Convention.

Fox's polls are included in those used by the Commission on Presidential Debates to determine whether either of the third-party candidates meet the 15% threshold needed to win a spot on the stage next month.

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