The track wheel with bladed spokes as shown in the photo was built for me in the late 1970s by a professional wheelbuilder. Note that the slots face inward on the hub flange, slanted along the axis of the spokes, such that there is no load on the slot and no reduction of flange material thickness on the pulling side of the spoke hole. These wheels have been used continously to this day in competition, without any failure or reduction in spoke tension. Note also that the spokes are tied and soldered where they cross, which was accepted practice for the day to presumably stiffen the wheel when accelerating, although current thinking is that this is unnecessary.