The Snap-on Flank Drive Xtra (FDX) Socket System is the first redesigned Snap-on socket since the patented Flank Drive system developed in 1965. Standout benefits include: up to 25 percent more strength than Flank Drive sockets; angled contour that grips damaged fasteners more closely; optimally chamfered lip on both the hex and drive ends of the socket for improved grip and turning power; grooved grippable outer walls; and large, distinctive markings on the socket exterior for easy identification.