The TrueTrainer comes with a 8-, 9-, 10-, 11- or 12-speed TrueKinetix cassette.
The 8- ,9- and 10-speed cassette have a 1.8mm spacer, so that it fits well. The spacer makes sure that the lockring correctly fixes the cogs on the hub.
8-, 9-, 10-speed cassettes all have the same spacing between cogs.
Supplied 11- &12-speed cassettes from TrueKinetix come without a spacer ring.