- A transmission device for splitting torque between two coaxial gears (14,15), in particular for a planetary gearing for aeronautic applications, the device comprising: - a motion input member; - a first and a second transmission member (36,37), which are coaxial to each other and to said motion input member along a longitudinal axis and comprise: a first shaft having a first gear at its axial end and a first intermediate portion, wherein said first shaft is formed by at least two pieces (58,59) which are coaxial and fixed to each other; a second shaft having a second gear at its axial end, wherein said second shaft is axially hollow and defines an inside diameter, wherein said first intermediate portion has an outside diameter smaller than said inside diameter of said second shaft and housed in said second shaft with radial clearance; a first flange, radially protruding outwards from said first shaft, at an axial end of the first flange opposite to said first gear; a second flange, radially protruding outwards from said second shaft, at an axial end of the second shaft opposite to said second gear, wherein the first and second flanges are axially facing and placed abutting against each other, and are fixed to said motion input member so as to split the torque transmitted from said motion input member between said first and second flanges; characterized in that, the device further comprising a first centring ring coupled around the first shaft and having an inside diameter equal to an outside diameter of a sleeve of the first transmission member, the first centring ring comprising a conical surface which is complementary to a corresponding conical surface of a coupling portion, wherein said second shaft ends with the coupling portion; and a second centring ring having an inside diameter equal to an outside diameter of a second intermediate portion of the first shaft, the second centring ring comprising a conical surface which is complementary to a corresponding conical surface of an end portion of the second shaft. - a motion input member; - a first and a second transmission member (36,37), which are coaxial to each other and to said motion input member along a longitudinal axis and comprise: a first shaft having a first gear at its axial end and a first intermediate portion, wherein said first shaft is formed by at least two pieces (58,59) which are coaxial and fixed to each other; a second shaft having a second gear at its axial end, wherein said second shaft is axially hollow and defines an inside diameter, wherein said first intermediate portion has an outside diameter smaller than said inside diameter of said second shaft and housed in said second shaft with radial clearance; a first flange, radially protruding outwards from said first shaft, at an axial end of the first flange opposite to said first gear; a second flange, radially protruding outwards from said second shaft, at an axial end of the second shaft opposite to said second gear, wherein the first and second flanges are axially facing and placed abutting against each other, and are fixed to said motion input member so as to split the torque transmitted from said motion input member between said first and second flanges; characterized in that, the device further comprising a first shaft having a first gear at its axial end and a first intermediate portion, wherein said first shaft is formed by at least two pieces (58,59) which are coaxial and fixed to each other; a second shaft having a second gear at its axial end, wherein said second shaft is axially hollow and defines an inside diameter, wherein said first intermediate portion has an outside diameter smaller than said inside diameter of said second shaft and housed in said second shaft with radial clearance; a first flange, radially protruding outwards from said first shaft, at an axial end of the first flange opposite to said first gear; a second flange, radially protruding outwards from said second shaft, at an axial end of the second shaft opposite to said second gear, wherein the first and second flanges are axially facing and placed abutting against each other, and are fixed to said motion input member so as to split the torque transmitted from said motion input member between said first and second flanges; a first centring ring coupled around the first shaft and having an inside diameter equal to an outside diameter of a sleeve of the first transmission member, the first centring ring comprising a conical surface which is complementary to a corresponding conical surface of a coupling portion, wherein said second shaft ends with the coupling portion; and a second centring ring having an inside diameter equal to an outside diameter of a second intermediate portion of the first shaft, the second centring ring comprising a conical surface which is complementary to a corresponding conical surface of an end portion of the second shaft.