This is a version of the 4-Wheel Tender that has, instead of conical sockets to accommodate the axles, cylindrical holes to take a metal bearing. In addition to wheels and a coupling, you will need to buy suitable bearings.
There is some variation between bearing manufacturers, and some variation in the tolerances of the prints, so you might need to do some filing or filling to get your bearings to work.
I have had success with Markits shouldered and top-hat bearings (without requiring any modification).
See the tender with coal
for further details.