The axle box comes in 3 parts: the casting, the brass, and the collar.
The casting is the main piece of the assembly:
The C-shape at the ends will receive the short and long wedges when the axle box is assembled into the frames.
The 3d view shows a recess at the top for oiling the axles. There are 2 holes that lead from this recess to the axle, but they’re not modeled yet.
The brass is the wearing surface of the axle box.
And the collar:
Here the axle box is assembled into the frame. The wedges are shown on either side of the axle box, and the pedestal cap closes the jaw at the bottom: