Shimano Dura-Ace CS-7800 10-speed Cassette 11t

"The new Dura-ace® 10 speed cassette is built to provide the best, most precise shifting imaginable. Designed to work with the 9-spd freehub, it is only 13 grams more than its 9-spd counterpart. The titanium sprockets have a special surface treatment increases durability by approx. 30%, making for a longer lasting drivetrain. Available in a variety of gear combinations to suit any rider for any situation, 11-21 and 11-23.For 12-21, 12-23, 12-25, 12-27 check out item # 50-2204"