A slotted set screw includes a slot in an upper end surface and a cut metal waste storing recess respectively formed at two ends of the slot. The cut metal waste storing recess is defined by a vertical wall and a flat bottom wall to have a large opening, separated from the slot for a little distance. The opening of the cut metal waste storing recess communicates with the outside of the threads of the set screw. Thus, cut metal waste may be stored in the cut metal waste storing recesses during cutting threads of the set screw and cannot fall into and remain in the slot to result in extra cleaning work for the waste in the slot.