The sleeve (20) has a part (22) including an axial bore (24) that receive a threaded maintaining pin (18), where the part is in external cylindrical shape, and periphery of the part is threaded for co-operating with a maintaining plate (12) of an osteosynthesis device. Another part (28) with an axial bore (30), is provided in an extension of the part (22), where thickness of the part (28) is less than that of the part (22). The part (28) is deformed so as to lock the sleeve on the maintaining pin. An independent claim is also included for an assembly comprising a locking sleeve and a ring.
