Thank you to all for the information.  The level of detail is great!!  NOW I KNOW.

I am relatively new to small scale model railroading.  I model N scale.

Is there any way to distinguish an F3 from an F7 from an F9?  I know the HP is different, but in model locos, this is a moot issue.  Are there any physical or appearance differences?  What does a passenger steam / power package look like?

Thank you in advance.

I just completed an N scale layout - my first ever "real" layout.  I used flex track.

9 inch radius is no problem.  6 inch or smaller is certainly possible.

You MUST solder joints on curves or they WILL misalign and cause derailments.  I suggest soldering the first two pieces  before installation.  I attached the track to the layout to about 2 inches from the track end.  Pin the end of the track in position and cut the long rail.  Pull the pins so the track tension is released and solder the next length to the existing track while both are straight.  Attack this length to the layout and repeat.  Joints on straight sections do not need soldered.  There are no forces trying to change the track alignment.

Flex track looks MUCH better than sectional track with many fewer joints and more design flexibility.

Thank You!  That is the information I needed.

They are all stock Bachmann, I assume Rapido couplers on freight cars.  On one, the coupler box is still attached with the spring still in place.

I am new to N scale. Where can I get  instructions  on how to fix or replace a coupler?