Abstract: A screw fastener and a tool for driving the screw fastener is disclosed. The screw fastener has a polygonal driving socket in its head, the driving socket having a substantially square first section and a second section including a rectangular slot radiating outwardly from the center of each side wall of the first section. The depth of the first and second sections are the same. Further, the screw fastener may be provided with internal ducts for conveying lubricant into a workpiece hole in which the fastener is being turned. A driving tool having a square shank for turning the screw fastener is also disclosed. One end of the tool's shank has a driving section comprising a rectangular fin extending longitudinally along and radiating outwardly from the center of each side wall of the shank. The shape of the driving section is complementary in shape to, and dimensioned to be snugly received in, the driving socket.