Abstract: An improved set screw with a break off head for use in an osteosynthesis apparatus. The set screw comprising a head or stem preferably having a hexagonal external cross-section, a lower portion having a thread extending around an outer surface thereof and a shank connecting the head to the threaded lower portion. An outer diameter of the shank is equal to a minor diameter of the threaded lower portion, i.e. the outer diameter of the threaded lower portion at the base of the thread. A bore extends into the set screw from an upper surface thereof. The bore has a first bore section and a second bore section wherein the second bore section has a reduced diameter relative to the first bore section and is separated from the first bore section by an internal shoulder. The internal shoulder extends into the bore below an upper end of the thread.