A quick coupling fitting (1) is described, comprising a first connector (2) and a second connector (3) coaxially screwed along a longitudinal axis (L), said first connector (2) comprises at least one guide track (27) which is integral with an external casing (23), a sliding ring (28) slidably mounted axially aligned with the external casing (23) and adapted to slide on said at least one guide track (27), a screwing ring (29) screwed with said external casing (23), said sliding ring (28) comprises at least one tooth (288), said second connector (3) comprises a locking ring (38) rotatably mounted axially aligned with said external body (3) which comprises at least one housing (388), said at least one tooth (288) being mountable with said at least one housing (388) in a fully screwed position of the quick coupling fitting (1).