A coupling system between the parts in a prosthesis for the articulation of the shoulder comprising a metal support, a pin element, a cylindrical bush and a glenosphere or hemispherical element which are consecutively coupled in the sequence listed above, in addition to reciprocal constraint elements, wherein said metal support is provided with a hole, said metal support and said pin element are constrained with an interposed conical coupling (13,14), the pin element being provided, externally at one of its ends, with a conical section, which engages with a complementary internal conical shape of the hole by means of a morse cone, wherein said pin element provides a central pass-through hole which comprises a threaded section, wherein said cylindrical bush is externally provided with a threading complementary to the threaded section of the pin element, wherein said glenosphere or hemispherical element comprises an axial pass-through hole having a first diameter, and further having on one side an internal seat with a second enlarged diameter provided with knurling, wherein said reciprocal constraint elements comprise at least one safety screw (23, 123) having a head (26, 126), wherein (i) said at least one safety screw is adapted to be screwed into an internal threaded portion of the cylindrical bush, or wherein (ii) the coupling system further comprises a central peg adapted to be coupled to the support, wherein said at least one safety screw is adapted to be screwed into a threaded hole in the interior of the central peg, wherein said pin element provides externally, at one end opposite to that of coupling with the metal support, a cylindrical section with a knurled surface, said knurling of the internal seat with the second enlarged diameter of the axial pass-through hole of the glenosphere or hemispherical element is complementary to the section with a knurled surface of the pin element, characterized in that the axial pass-through hole has a section with a third enlarged diameter on the opposite side of the internal seat having the second enlarged diameter, wherein the head (26, 126) of the at least one safety screw (23, 123) is adapted to be arranged in said section with the third enlarged diameter of the axial hole of the glenosphere. said metal support and said pin element are constrained with an interposed conical coupling (13,14), the pin element being provided, externally at one of its ends, with a conical section, which engages with a complementary internal conical shape of the hole by means of a morse cone, wherein said pin element provides a central pass-through hole which comprises a threaded section, wherein said cylindrical bush is externally provided with a threading complementary to the threaded section of the pin element, wherein said glenosphere or hemispherical element comprises an axial pass-through hole having a first diameter, and further having on one side an internal seat with a second enlarged diameter provided with knurling, wherein said reciprocal constraint elements comprise at least one safety screw (23, 123) having a head (26, 126), wherein (i) said at least one safety screw is adapted to be screwed into an internal threaded portion of the cylindrical bush, or wherein (ii) the coupling system further comprises a central peg adapted to be coupled to the support, wherein said at least one safety screw is adapted to be screwed into a threaded hole in the interior of the central peg, wherein said pin element provides externally, at one end opposite to that of coupling with the metal support, a cylindrical section with a knurled surface, said knurling of the internal seat with the second enlarged diameter of the axial pass-through hole of the glenosphere or hemispherical element is complementary to the section with a knurled surface of the pin element, characterized in that the axial pass-through hole has a section with a third enlarged diameter on the opposite side of the internal seat having the second enlarged diameter, wherein the head (26, 126) of the at least one safety screw (23, 123) is adapted to be arranged in said section with the third enlarged diameter of the axial hole of the glenosphere.