TT Scale. The Ideal Scale.

Here is a good source of information/dimensions for Railway cars, trucks etc.
You can find an older version on Google Books. The copyright has expired and it is in the public domain.

Car Builders Dictionary and Cyclopedia 1919 edition online:
http://ebook.lib.hku.hk/CADAL/B3139551X

now that is a very good link thanks for posting it

Indeed. It'll be added to the links sticky shortly.......

I just barely missed out on getting a copy of the 1946 CBC. A friend of mine has one from the 1940s, too, and the Vancouver Public Library has a 1953 edition... I still want to try and get my hands on a copy from 1940-1950 or so, they're an amazing resource!