The XW4548 (865-1005) is the only XW that ships with the ferrite rings. It also ships with an addendum to describe how to install them. The addendum number is 976-0185-01-01 and attached here for reference. The ferrite rings are there to reduce noise emissions at a very specific frequency. At 41MHz these ferrites reduce the radiated noise by about 6 [dB*uV]. Other than this frequency they do not have any other impact in emissions or unit functionality.