When you look at a piece of Z-Scale track on a Z-Scale layout, the track sections represent real track which is Standard Gauge, with the rails being spaced 4’ 8 1/2” apart. There are a few Internet pages that attribute this odd size to the spacing of the wheels of Roman chariots; we will leave discussion of why the Gauge is what it is for another day. It is what it is, and most of the world uses this gauge.
There are interesting exceptions. Japan, for instance uses a track gauge of 3’ 6”, with their Shinkansen high speed trains operating on 4’ 8 1/2”. In this case, 3’ 6” is their Standard Gauge and 4’ 8 1/2” is Wide Gauge. There are some examples of wide gauge in the United States, such as certain streetcar systems that were deliberately built wide to keep standard gauged steam trains from operating on city streets. But, in most cases, what you see is likely to be Standard Gauge.
Of course, railroading is infinitely interesting and infinitely adaptable, which brings us to Narrow Gauge. Although there are still extant examples of narrow gauged railroads in America, they are not as common as they once were. In the 1800’s, there was a lot of experimentation with different track gauges, and there were passionate proponents of these different gauges. In America, one narrow gauge that caught on was 3’ Gauge, your basic yardstick gauge. There were instances of 3 foot gauge all over the country, but the gauge was especially popular in Colorado. To be sure, there were lots of other examples, such as the East Broad Top in Pennsylvania, the Southern Pacific had narrow gauge in California and Nevada. The Roswell Railroad in Georgia was initially built to three foot gauge. But the really holy place is Colorado.
Narrow gauged trains had certain financial advantages. Construction was less expensive than a standard gauge railroad. The equipment was smaller yet the narrow gauge railroad retained the advantages of steel wheel on steel rail. Bridge and tunnel construction costs were lower, too. In the early days, when all was sunny and bright, the narrow gauged lines had colorful locomotives and cars. Later, when things were starting to decline, the equipment took on a delightful weather beaten appearance, making them irresistible to model railroaders.
So, when you see a piece of Z-Scale track in an N-Scale environment, you are looking at track which approximates the three foot gauge commonly found in Colorado. This offers some distinct advantages. Locomotives can be cobbled up by using Märklin or Micro-Trains mechanisms. N-Scale structures are plentiful, and many of them are based upon known narrow gauge prototypes. To differentiate this sort of train from ordinary N-Scale, we use the term Nn3, which stands for N-Scale (narrow gauge of three feet). There are other “n’s” that use track from another scale; two other common ones are H0n30 and 0n30. In particular, 0n30 is a very active part of the model railroad hobby.
Getting back to Nn3, consider this scene: