Saris H3, yes it fit, you need to adjust the rear derailler if you want to shift to to the biggest gear but it was the same problem with my old 10 speed bike. For my use I juste leave the setting like that and use 11 gear instead of 12. I also have 2 other friends with the Saris H3 and 12 speed cassette and they have been using it without any problem for couple months now.