WhisperDrive Freehub Body Shimano/SRAM

The JetBlack WhisperDrive is the first direct-drive indoor trainer compatible with 12x143mm thru-axle bikes.

Direct drive, of course, means your bike connects directly to the trainer, rather than your rear wheel turning a roller. The JBT-75A Freehub Body with 10 Speed Spacer is specifically designed for the WhisperDRIVE indoor trainer.