Shimano Tiagra CS-HG50 Cassette

9-speed performance from precision made HG sprockets and ultra-narrow chain. No increase in sprocket cluster width allows retrofit to 8-speed freehubs. Computer-designed HG (HyperGlide) sprockets insure fast and quiet down-shifts as well as instant up-shifts without hesitation.
The 9-speed sprockets are made to the same specifications as those used in the 9-speed Dura-Ace, Ultegra, and 105 groups, so there's complete interchangeability.
Features:
High quality 9-speed Road cassette
Hyperglide sprockets have a computer designed tooth configuration with contoured shift gates, resulting in a crisp smooth shift even under load
Close ratio gearing allows a more efficient use of energy through finer cadence control
Sprockets are cut away and drilled to reduce weight without reducing rigidity
Nickel-plated finish offers hard wearing resistance to corrosion
Corrosion-resistant steel cassette lockring
For Super Narrow 9-speed HG chains