S scale’s rail code heights are: .070, .083, .100, and .125. Locomotive, tender and rolling stock are narrow wheeled, utilizing the code-125, and or 110, S scale wheels. With the addition of S scale trucks and knuckle couplers, you’ve defined a true S scale configuration with an enhanced appearance and operational accuracy. Active and past S scale locomotive and rolling stock manufacturers tend to depict finite detail on their models,
this being one of the main reasons for S scale's popularity. For a true S scale layout, structures also need to be S scale.