"The standard body of a Tacx direct drive trainer is not compatible with all cassettes. Use this body to mount your SRAM XD-R cassette. It’s easy to install, and all you’ll need is a 5 mm hex key.
 
The SRAM XD-R body is compatible with 11- and 12-speed SRAM XD-R cassettes. This version is used for trainers with Type 2 axles."