The conical pin end of the male endoprosthesis part is provided with a deformable surface while the conically recessed articular ball is provided with inwardly directed lugs for penetrating into the deformable surface during mounting on the pin end. The lugs have a maximum height of 0.5 millimeters and a maximum width of three millimeters. The deformable pin surface may be formed by a screw thread, a plurality of circumferential grooves of wavy configuration or a plurality of circumferential ribs.