Over time, the number of sprockets in a cogset has increased, from three or four before World War II, to five used from the 1950s to the 1970s, up to the eight, nine, ten, eleven, or twelve now found on modern bikes. As more rear sprockets were added, the combination became wider, and the sprocket spacing narrower. One of the ways to make space for this was the axle length (measured as the Over Locknut Distance — O.L.D.) was increased, necessitating more dish on the rear wheel drive side with a threaded hub to centre the wheel in the frame. The hub flanges spacing was not shortened on threaded hubs, rather the axle length increased from 120 mm O.L.D. (five-speed/compact six) to 126 mm O.L.D. (six-speed/compact seven) through to 130 mm O.L.D. (threaded seven-speed) for a road bike. MTB rear spacing is normally 135 mm O.L.D. Another advantage of the Shimano cassette hubs introduced from 1978 was that the rear hub flanges were wider apart than those of a threaded hub, so built a stronger wheel with less dish and without the problem of increased bearing stress or axle failure.