Ultegra CS-6600 cassettes with a 13???16-tooth first-position cog are notcompatible with Dura-Ace FH-7800 hub or WH-7800 wheel
Compatible with all 10- and 9-speed Shimano hubs except for 13???16-toothfirst position cog cassettes which are not compatible withDA FH-7800 hubs or WH-7800 wheels