To provide a screw with cut-in portions, a nut and a driver, wherein a high safety is attained since mounting and demounting are hard if an exclusive tool is not used, the screw or a bolt is hard to drop off since it is held between projections provided at a tip of the driver, thereby attaining a high work efficiency, a wear resistance is increased to make hard generation of looseness since there is the cut portions on the outer circumferential part of a top of the mounted screw or the bolt, and the screw or the bolt when demounted, are prevented from dropping since they are held by the projections on the tip of the driver.

Three cut-in portions are formed on the outer circumferential part of a top of a screw or a bolt. The screw or bolt is held between three projections on a tip of an exclusive-use driver inserted into the three cut-in portions. Thereby it is possible to lead the screw or bolt to a target position without the support of a hand or fingers. The screw or bolt can be fastened by turning the driver. The fastened screw or bolt is hard to be loosened by the aid of the cut-in portions fitted to the projections of the driver. In demounting the screw or bolt, it can be easily demounted by turning the driver. At this time, it is prevented from dropping off by the aid of the projections.