The following freight cars are "oddly" sized:
Slagcar: The pivoting hopper section is "7-wide".
The support beam beneath the hopper section is "studs-down".
Blue and white hopper: Yup, "7-wide".
Pneumatic hopper: This one is "7-wide". It is also an odd length at 15 studs
long between the buffers. This "15-long" construction centers the 4-to-a-side
hopper bins with respect to the wheels.