September is sitting pretty at the box office, with record domestic returns thanks to such recent R-rated films as the Taron Egerton-starring “Kingsman: The Golden Circle.” (Twentieth Century Fox)

AS THE WEEKEND’S top three domestic films duke it out within a hairbreadth of each other commercially, there’s a larger convergence to notice.

The surprise is not that the Stephen King horror hit “It,” the Tom Cruise crime thriller “American Made” and Matthew Vaughn’s comic-book sequel “Kingsman: The Golden Circle” each grossed $17 million over the box-office weekend, with Monday afternoon’s final numbers still to decide the actual box-office champ. No, the most striking aspect is that all three top films in North America are rated “R.”

Yes, mature filmgoers, Hollywood has fully rediscovered the marketable R-rated film.

For the second time in three weeks, in fact, R-rated films hit the domestic trifecta, with “It,” Michael Keaton’s “American Assassin” and Jennifer Lawrence’s “mother!” topping the charts — just one week after “It,” “The Hitman’s Bodyguard,” “Annabelle: Creation” and “Wind River,” all rated R, dominated the previous weekend’s top five.

The massive “It,” which has grossed nearly $300 million domestically and $553 million worldwide (on a $35 million production budget), also led the highest-grossing domestic September ever ($695 million), not adjusting for inflation.

This isn’t just a September trend. The larger picture is that year to year, Hollywood has decided that the R rating is no longer the barrier to mass popularity that it recently was perceived to be.

Consider: In 2016, only a lone R-rated film (“Deadpool”) cracked the year’s top 24 movies in North America.

In 2017, however, that total has soared to eight: “It,” “Logan,” “Get Out,” “Girls Trip,” “Fifty Shades Darker” “Baby Driver,” “Annabelle: Creation” and “John Wick: Chapter 2″ — with three more R-rated films, “The Hitman’s Bodyguard,” “Alien: Covenant” and “Kingsman: The Golden Circle” rounding out the year’s top 30.

Expand that list to North America’s top 40, and four more R-rated movies — “Baywatch,” “Atomic Blonde,” “Snatched” and “All Eyez on Me” — enter the picture, meaning that 15 of the year’s 40 biggest films are more mature than a PG-13 rating.

Just what is happening here? Well, part of the confluence includes:

* The conventional wisdom that superhero films typically need a PG-13 rating to succeed (2008’s “The Dark Knight” is truly R-rated fare than somehow secured a PG-13 rating to play it commercially safe) has been upended by such recent smashes as “Deadpool” and “Logan.” Even before that, the first “Kingsman” helped reflect the true appetite for R-rated comic-book adaptations.

* “Get Out” and “It” have reminded Hollywood that smart R-rated horror can crack the quarter-billion-dollar tally.

* Disney might have two of the year’s three biggest hits in “Beauty and the Beast” (PG) and “Guardians of the Galaxy: Vol. 2″ (PG-13) — with the latest “Star Wars” still to come — but such studios as Fox, Universal and Warner Bros.’s New Line are mining the “R” market for great riches.

And all this bodes well for the next big R-rated film, Warner Bros.’s already critically acclaimed “Blade Runner 2049″ (opening Friday), which could reflect just how high the R-rated ceiling is in 2017.

This post has been updated.

Read more:

How ‘Deadpool’ has redefined the future of the R-rated superhero film

How ‘Kingsman: The Golden Circle’ beat ‘The Lego Ninjago Movie’ in a battle of franchises