A bone fixation system includes a bone plate and a bone screw having a threaded head. The inner surface of the bone plate is adapted for facing a bone surface on which the plate is mounted. The outer surface of the bone plate faces away from the bone surface. A through opening extends from the inner surface to the outer surface of the plate wherein the through opening comprises a guiding portion and a blocking portion. The guiding portion of the opening is provided with a guiding thread for guiding a thread of a shaft of the bone screw. The blocking portion is provided with a blocking thread for blocking a thread of the head of the bone screw. The blocking thread has a larger diameter than the guiding thread and the guiding portion is located closer to the inner bone plate surface than the blocking portion.
