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Ok these are a bit odd, but once explained they make some sense. Back in the days before shimano 9 speed groups you could take an 8 speed cassette not mounted on a carrier, drive out the rivets or unscrew the pins and end up with 8 cogs and a couple spacers. Mount one of these dished 33t cogs on then freehub, then your 11x28 8 speed cassette and you have a 9 speed cassette spaced like an 8 speed. Hook up ritchey 2x9 shifters item YS-GS2X9LR and POOF! You have a nine speed mountain bike. The tinkering possibilities are endless.