Shimano CS-6600 Ultegra Cassette ****Has been discontinued and replaced with the CS-6700.

the Ultegra CS-6600 cassette's 10-cog stack is no thicker than the CS-6500 9-speed version. This is a versatile cassette and is  fully compatible with a Dura Ace 7800 10-speed drivetrain. It's also compatible with any Shimano 9-speed generation hub.

The 11-23 includes- 11,12,13,14,15,16,17,19,21,23
The 12-23 includes- 12,13,14,15,16,17,18,19,21,23
The 12-25 includes- 12,13,14,15,16,17,19,21,23,25
The 12-27 includes- 12,13,14,15,16,17,19,21,24,27