The utility model provides a lower universal screw of binding formula, relates to the technical field of medical equipment, including screw base and bulb screw, be equipped with continuous lower ball socket and last ball socket in the pilot hole of screw base lower part, the diameter of going up the ball socket is greater than ball socket diameter down, in the pilot hole assembly income screw base of bulb by lower ball socket below of bulb screw, down in the ball socket, the bulb downside of bulb screw is equipped with one side opening, elastic spherical ring has, the bulb and the spherical intra-annular sphere matched with of bulb screw assemble at spherical intra-annular, the spherical outside surface and the lower ball socket of spherical ring cooperate, be equipped with the location clamping ring that compresses tightly the bulb in the pilot hole on the bulb upper portion of bulb screw, be equipped with the internal thread on the screw base inner wall of U-shaped groove both sides. The utility model discloses simple structure, convenient assembling, nail body diameter is big, the swing angle is big, the bulb face contact of spherical ring and bulb screw, the atress is even, difficult fracture, the structure is firm, and application scope is wide, is particularly useful for the fixed operation of ilium.