I have read a lot of historical books and they always refer to trains as 4-6-2, 0-4-2, 0-4-0…etc. I always wondered what that meant. Is it the size of the engine, some short designation of the manufacturer? So, I researched it. Below are excerpts from the best page on it I have found. Don’t hate because it is on Wikipedia…it is much better than the other sources. The complete link at the end.
Here we go…
The Whyte notation for classifying steam locomotives by wheel arrangement was devised by Frederick Methvan Whyte[2] and came into use in the early twentieth century, encouraged by an editorial inAmerican Engineer and Railroad Journal (December 1900). The notation counts the number of leading wheels, then the number of driving wheels, and finally the number of trailing wheels, groups of numbers being separated by dashes.[3] Other classification schemes, like UIC classification and the French, Turkish and Swiss systems for steam locomotives, count axles rather than wheels.
In the notation a locomotive with two leading axles (four wheels) in front, then three driving axles (six wheels) and then one trailing axle (two wheels) is classified as 4-6-2.
http://en.wikipedia.org/wiki/Whyte_notation
Michael Bradley - Time Traveler 