Locking system for securing a rod in a channel rod receiving a device polyaxial bone anchoring for use in surgery spinal or trauma column, said locking system comprising a first locking element (9) with a first end (91) and a second end (92), a longitudinal axis of rotation (C) and an outer surface portion with an external thread (93), a coaxial bore extending through said first locking element, an internal thread (94 ) provided in a portion of said bore and a coupling portion (95, 96) for an actuating tool in order to rotate the first blocking element, a second locking element (10) having a first end (101) , facing the first end (91) of the first locking element and a second opposite end (102), an outer surface portion with an external thread (103a) cooperating with the internal thread (94) of the first locking element characterized in that the second locking element comprises a portion (105) prevents the second locking element to rotate when inserted into the receiving channel rod (12) of the bone anchoring device, the second locking member being configured (10 ) so that when the first locking element (9) is rotated to move in a first axial direction, to move relative to the first locking element (9) in an opposite axial direction.Sistema de bloqueo para asegurar una varilla en un canal de alojamiento de varilla de un dispositivo de anclaje óseo poliaxial para su uso en la cirugía de la columna vertebral o traumatológica, comprendiendo dicho sistema de bloqueo un primer elemento de bloqueo (9) con un primer extremo (91) y un segundo extremo (92), un eje longitudinal de rotación (C) y una parte de superficie exterior con una rosca externa (93), un taladro coaxial que atraviesa dicho primer elemento de bloqueo, una rosca interna (94), prevista en una parte de dicho taladro y una parte de acoplamiento (95, 96) para una herramienta de accionamiento con el fin de girar el primer elemento de bloqueo, un segundo elemento de bloqueo (10) con un primer extremo (101), orien
