An insert (11) of a joint ball receptacle of a prosthetic shoulder joint according to the invention has a first side (I) with a depression (15) for receiving a joint ball, and a second side (II) which is provided and formed for being received in a shell (13) of the joint ball receptacle. According to the invention, a snap action mechanism (19) which extends around a central axis (17) of the insert (11) is arranged on the second side (II), which snap-action mechanism (19) has, as seen from the second side (II), and together with a collar (21), an undercut (23) which extends around the central axis (17), in such a way that the collar (21) can engage with elastic deformation behind a correspondingly formed mating element (25) of the shell (13), wherein the snap-action mechanism (19) is discontinuous in the peripheral direction of the insert (11) at at least one point (31); according to the invention, the insert (11) has a cylindrical guide region (27) at the outer periphery in the region provided for being received in the shell (13).