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. Before the introduction of indexed shifting, the width of a five-speed or compact six freewheel was approximately 32 mm; the introduction of indexed shifting supposedly made standardized sprocket spacing necessary. Shimano and Campagnolo both came up with independent standards, and SRAM later followed Shimano's lead in respect to sprocket spacing and cassette width. The width of early Shimano six- and seven-speed cassettes was 36 mm, and early eight-speed 40 mm wide. Shimano then changed again and standardised eight-eleven speed cassettes on 41.5 mm and second generation seven-speed to 38 mm. The widening of the sprocket carrier on the cassette hubs to 41.5 mm resulted in a decrease in the distance between the hub flanges. For Shimano and SRAM the cassette spacing developed as follows. Early Shimano seven-speed cassettes are 36 mm wide, with sprocket spacing of 3.65 mm, but levers and rear derailleurs are not compatible with later Shimano seven-speed cassettes, which are 38 mm wide and have 3.2 mm sprocket spacing. An eight-speed cassette is wider at 41.5 mm than a second generation Shimano seven. This results in functionally compatible shifters, but specific freehub bodies, or necessitating the use of a spacer with a seven-speed cassette on an eight-speed hub. Eight- and nine-speed cassettes and freehub bodies have the same width (41.5 mm), yet the sprockets on the nine-speed are closer together; as a result the shifters are not compatible, but they use the same freehub bodies. This development continued with ten-speed cassettes, but