center-bearing

from The Century Dictionary.

• noun In carbuilding, the chief system of supporting the weight of a car upon its truck: distinguished from a side-bearing, or a fixed bearing, as in a small car having no trucks; also the place where the weight of the car-body rests upon the center-plates and where the center-pin joins the car to the truck. The center-bearing beam is the beam which supports the truck center-plate and, in six-wheel trucks, is supported by the center-bearing bridge. See body center-plate, center-plate block, and cut under car-truck.