To use a 12-speed SRAM Apex cassette (mechanical) on the roller trainer, you need the SRAM XDR Freehub adapter, as SRAM 12-speed cassettes use the XDR freehub body system. A 1.8 mm spacer for XD compatibility is also included in the adapter kit. The original lockring is replaced by a suitable conical lockring included in the kit.

In concrete terms, this means
- Remove the existing Shimano-compatible freehub body.
- Install the SRAM XDR freehub adapter.
- Fit the SRAM 12-speed cassette to the XDR Freehub.
- Use the supplied lockring from the adapter kit.

This ensures compatibility with the SRAM Apex 12-speed cassette. Note that the conversion requires tools such as a chain whip, lockring spanner and adjustable spanner.