A connecting device for connecting together two separate mechanical parts (P1, P2), said device comprising: - a rod having a longitudinal axis (X-X) and comprising a section intended to be inserted at least partly into aligned clevises (2, 3) of said mechanical parts (P1, P2), said section extending between an axial stop and a threaded portion of the rod, - a nut configured to be screwed onto said threaded portion of said rod so as to hold said two mechanical parts (P1, P2) between said axial stop and said nut, and - an anti-rotation system configured to block in rotation said nut, said anti-rotation system comprising: ∘ a washer mounted around said rod and configured to cooperate by complementary shapes with said rod so that said washer is secured in rotation to said rod, said washer comprising at least one protuberance extending inwards with respect to said longitudinal axis (X-X), the or each protuberance being engaged in a notch of complementary shape in said rod, and ∘ a ring mounted around the nut, said ring comprising an internal periphery complementary in shape to that of an external periphery of said nut so that said ring is secured in rotation to said nut, characterised in that said anti-rotation system also comprises a screw which is configured to ensure that said ring and said washer are secured axially in rotation, and in that said ring also comprises: - an axial slot to minimise the mounting clearance on said nut, - two circumferential ends (17A, 17B) which are located on either side of said axial slot, each of said circumferential ends (17A, 17B) extending into an attachment tab (18A, 18B) comprising a central orifice (19A, 19B) for the passage of said screw, said washer comprising a protrusion configured to be interposed between said tabs (18A, 18B), said protrusion comprising an orifice for the passage of said screw. - a rod having a longitudinal axis (X-X) and comprising a section intended to be inserted at least partly into aligned clevises (2, 3) of said mechanical parts (P1, P2), said section extending between an axial stop and a threaded portion of the rod, - a nut configured to be screwed onto said threaded portion of said rod so as to hold said two mechanical parts (P1, P2) between said axial stop and said nut, and - an anti-rotation system configured to block in rotation said nut, said anti-rotation system comprising: ∘ a washer mounted around said rod and configured to cooperate by complementary shapes with said rod so that said washer is secured in rotation to said rod, said washer comprising at least one protuberance extending inwards with respect to said longitudinal axis (X-X), the or each protuberance being engaged in a notch of complementary shape in said rod, and ∘ a ring mounted around the nut, said ring comprising an internal periphery complementary in shape to that of an external periphery of said nut so that said ring is secured in rotation to said nut, ∘ a washer mounted around said rod and configured to cooperate by complementary shapes with said rod so that said washer is secured in rotation to said rod, said washer comprising at least one protuberance extending inwards with respect to said longitudinal axis (X-X), the or each protuberance being engaged in a notch of complementary shape in said rod, and ∘ a ring mounted around the nut, said ring comprising an internal periphery complementary in shape to that of an external periphery of said nut so that said ring is secured in rotation to said nut, characterised in that said anti-rotation system also comprises a screw which is configured to ensure that said ring and said washer are secured axially in rotation, and in that said ring also comprises: - an axial slot to minimise the mounting clearance on said nut, - two circumferential ends (17A, 17B) which are located on either side of said axial slot, each of said circumferential ends (17A, 17B) extending into an attachment tab (18A, 18B) comprising a central orifice (19A, 19B) for the passage of said screw, said washer comprising a protrusion configured to be interposed between said tabs (18A, 18B), said protrusion comprising an orifice for the passage of said screw. - an axial slot to minimise the mounting clearance on said nut, - two circumferential ends (17A, 17B) which are located on either side of said axial slot, each of said circumferential ends (17A, 17B) extending into an attachment tab (18A, 18B) comprising a central orifice (19A, 19B) for the passage of said screw, said washer comprising a protrusion configured to be interposed between said tabs (18A, 18B), said protrusion comprising an orifice for the passage of said screw.