We do assemble the wheelset from components. So (obviously), an axle, 2 loose wheels, and 2 bearings.
Wheels come back on the same flat that they were sent out on and those either need a simple turning (with 2 new/recon bearings also applied) or, more often than not, they get fully demounted, axles get reworked, new loose wheels are applied, and new bearings are applied. We'll do about 100,000 per year, most getting the full demount.