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. Ten-speed cassettes are slightly more "narrow" than eight/nine so they fit on those freehubs but need a spacer, conversely eight/nine-speed cassettes do not fit on ten-speed freehubs.