If you want to put a Roadmaster tow bar (some models, at least) on a Blue Ox or Demco baseplate, you need to put the Blue Ox connectors on the tow bar, as shown.
If you want to use a Blue Ox, Demco, NightShift Auto, or similar tow bar on Roadmaster towing brackets, then you need an adapter, cross-piece with tabs actually, that mounts on the Roadmaster brackets and converts it to a base plate.
The adapters add enough to the cost so that it is often not economic to mix styles (Roadmaster vs everybody else) but there might be another reason to do it, i.e. the car already has Roadmaster brackets installed, or you don't like the way somebody's base plate installs.
The latter was my reason for choosing BlueOx for my Honda Fit, since it installed behind the bumper core, while the Roadmaster installation required permanent removal of the bumper core.