Shimano's 11-speed hubs obviously fit Shimano and SRAM 11-speed cassettes but they also accept 8, 9 and 10-speed cassettes with an appropriate spacer. I'm not sure but I believe the spacer comes with the hubs. If not, any bike shop should be able to get one for you. Those hubs will even accept a 7-speed cassette with an additional spacer but the spacer stack gets a bit awkward at that point.