An anti-torque rotor (4; 4'; 4") for a helicopter, comprising: - a mast, rotatable about a first axis; - a plurality of blades, hinged on said mast, extending along respective second axes transversal to said first axis and rotatable about respective said second axes to vary the respective angles of attack; - an element, sliding along said first axis with respect to said mast, integrally rotating with said mast, and operatively connected to said blades to cause the rotation of said blades about respective said second axes following a translation of said element along said first axis; - a control rod, sliding axially along said first axis with respect to said mast and angularly fixed with respect to said first axis; - a first ring (30; 30") rotatable integrally with said element about said first axis; - a second ring (50; 50") sliding integrally with said control rod along said first axis and angularly fixed with respect to said first axis; and - a third ring (31; 31"); - a plurality of first rolling bodies (32; 32"), which are interposed between said first and third rings (30, 30"; 31, 31") and adapted to roll on respective first tracks (33, 34; 33", 34") of said first and third rings (30, 31; 30", 31"); - a plurality of second rolling bodies (51; 51"), which are interposed between said second and third rings (50, 31; 50", 31") and adapted to roll on respective second tracks (52, 53; 52", 53") of said second and third rings (50, 31; 50", 31"); and - a locking element (55; 55") arranged in a standard configuration, wherein it allows the relative rotation of said third ring (31; 31") and one of said first ring and second ring (30, 50; 30", 50"); said locking element (55; 55") being movable from said standard configuration to at least one emergency configuration, wherein it allows the relative rotation of said third ring (31; 31") and the other one of said first ring and second ring (30, 50; 30",50"); said first ring (30; 30"), said third ring (31, 31") and said second ring (50, 50") being coaxial and extending about said 2. first axis; said second ring (50, 50") being radially internal with respect to said third ring (31, 31"); said third ring (31, 31") being radially internal with said first ring (30, 30"); said first tracks (33, 34; 33", 34") radially facing one another; said second tracks (52, 53; 52", 53") radially facing one another; characterized in that said third ring (31, 31") defines in a one piece one of said second tracks (52, 53; 52", 53") and one of said first tracks (33, 34; 33", 34"); said first tracks (33, 34; 33", 34") and said second tracks (52, 53; 52", 53") radially facing one another. - a mast, rotatable about a first axis; - a plurality of blades, hinged on said mast, extending along respective second axes transversal to said first axis and rotatable about respective said second axes to vary the respective angles of attack; - an element, sliding along said first axis with respect to said mast, integrally rotating with said mast, and operatively connected to said blades to cause the rotation of said blades about respective said second axes following a translation of said element along said first axis; - a control rod, sliding axially along said first axis with respect to said mast and angularly fixed with respect to said first axis; - a first ring (30; 30") rotatable integrally with said element about said first axis; - a second ring (50; 50") sliding integrally with said control rod along said first axis and angularly fixed with respect to said first axis; and - a third ring (31; 31"); - a plurality of first rolling bodies (32; 32"), which are interposed between said first and third rings (30, 30"; 31, 31") and adapted to roll on respective first tracks (33, 34; 33", 34") of said first and third rings (30, 31; 30", 31"); - a plurality of second rolling bodies (51; 51"), which are interposed between said second and third rings (50, 31; 50", 31") and adapted to roll on respective second tracks (52, 53; 52", 53") of said second and third rings (50, 31; 50", 31"); and - a locking element (55; 55") arranged in a standard configuration, wherein it allows the relative rotation of said third ring (31; 31") and one of said first ring and second ring (30, 50; 30", 50"); said locking element (55; 55") being movable from said standard configuration to at least one emergency configuration, wherein it allows the relative rotation of said third ring (31; 31") and the other one of said first ring and second ring (30, 50; 30",50"); said first ring (30; 30"), said third ring (31, 31") and said second ring (50, 50") being coaxial and extending about said 2. first axis; said second ring (50, 50") being radially internal with respect to said third ring (31, 31"); said third ring (31, 31") being radially internal with said first ring (30, 30"); said first tracks (33, 34; 33", 34") radially facing one another; said second tracks (52, 53; 52", 53") radially facing one another; characterized in that said third ring (31, 31") defines in a one piece one of said second tracks (52, 53; 52", 53") and one of said first tracks (33, 34; 33", 34"); said first tracks (33, 34; 33", 34") and said second tracks (52, 53; 52", 53") radially facing one another.