Shimano HG50 9-Speed CassetteThe Hyperglide HG50 9-Speed Cassette plays a key role in enabling Shimano's trademark smooth gear shifting.The Hyperglide sprocket's computer designed tooth configuration, with its cutaways and contoured shift gates, delivers crisp, smooth gear shifting - even under load.The sprockets are drilled to reduce weight without reducing their strength and rigidity.The cog's nickel-plated finish offers hard wearing resistance to corrosion.The steel cassette lockring, which keeps the cogs in place, is also corrosion resistant.Designed to work best with a Super Narrow 9-speed HG (Hyperglide) chain.