Abstract: A locking device (5) of a bone screw (3) for an external fixator (1) for bone fractures is described herein, wherein the external fixator (1) comprises at least one support pin (202). The locking device (5) comprises a locking element (501) of the bone screw (3); a locking pin (502), which is configured to support the locking element (501), the locking element (501) being configured to rotate around the blocking pin in a bone screw positioning step; a coupling element (503), which is provided with a respective coupling seat (503b) configured to receive the support pin (202) by snap-fit coupling and to allow, during the bone screw (3) positioning step, a rotation of the locking device (5) around the support pin (202) and a sliding of the locking device (5) along the support pin.