High torque transmission fastener and driving tool therefor

A fastener comprising:

• a screw head including a driven protrusion that has four driven wall portions and four guiding wall portions which are disposed about a central axis of the fastener in an alternating arrangement, the driven wall portions being equiangularly spaced apart from each other, each of the guiding wall portions being straight and having two opposite ends that are respectively connected to two of the driven wall portions adjacent to the guiding wall portion, a ratio of a longest distance between two of the driven wall portions that are non-adjacent to each other to a longest distance between two of the driven wall portions that are adjacent to each other being greater than 1.16, each of the driven wall portions having a curved section that defines an arc of a circle and that has two opposite ends, and two straight sections each of which extends from a respective one of the ends of the curved section and interconnects the respective one of the ends of the curved section and a respective one of two of the guiding wall portions adjacent to the driven wall portion, a central angle of the curved section of each of the driven wall portions being smaller than 180 degrees;
• and
• a screw shank extending from one side of the screw head that is distal from the driven protrusion of the screw head in an axial direction of the central axis, and having at least one thread that helically extends therealong.