Model trains come in a wide variety of sizes, or scales, from garden all the way down to the diminutive z scale trains. One of the more popular model train scales in the US is O Scale, or "zero" scale. Within this category, there are actually a variety of sizes standards and track gauges, or widths, to choose from. If you are considering a particular train model in this size range, then it is important to understand the differences between the various O scale standards and gauges to ensure that the train you buy is compatible with your existing or envisioned setup. This article will explain the history of O scale trains, the various O scale size standards that are in use today, and the various track gauges that are associated with them in the US.
History of O Scale Trains
O scale or 0 gauge trains have actually been around since the early 1900s when they were first introduced in Europe by Marklin. The term O scale is derived from the original 0 [zero] gauge or Gauge 0, so named because it was smaller than existing model train standards such as Gauge 1. In the US, O scale sized model trains were promoted by early manufacturers such as American Flyer and Lionel Corporation as their relatively inexpensive budget lines. 0 gauge trains became quite popular, primarily because of their lower cost when compared to the larger sized trains of the time. The Great Depression eventually wiped out demand for the larger, more expensive model trains, and by 1932, 0 scale became the dominant size standard (almost by default). Since the initial introduction of 0 scale trains, a number of different 0 scale sizes and gauges have become standardized. These terms are often used interchangeably, but actually have different meanings. Scale refers to the size of the model train relative to the real life train being represented. Gauge refers to the width of the model tracks.
As it turns out, there are multiple size or proportion standards for O scale trains. The original European standard is 1:45, which means 1" on the model is equal to 45" on a real train. In the UK, the O scale standard is 1:43.5, or 7mm to the foot. In the US, the National Model Railroad Association (NMRA) standard for O scale trains is 1:48 or 1/4" to the foot. So, a 48 foot long real diesel locomotive modeled in 1/4" O scale would be 12" long. In comparison, the same 48 foot diesel would be 12.8" long in the European standard and 13.2" long in the UK standard. The majority of US manufacturers offer their O scale model lines in the 1/4" O scale (1:48) standard.
Once you have selected your O scale size standard, you still have to make sure your track gauge is compatible with your model train. If you recall we said previously that gauge refers to the width of the model tracks. In the US, the NMRA recognizes four track gauges in 1/4" O scale. The most popular gauge, and also the largest in width, is the 1.25" gauge. The 1.25" gauge is referred to simply as O scale. The next most popular gauge is On30. On30 model trains are basically 1/4" O scale trains which run on HO scale track. In between O scale and On30 is On3 which is a 3/4" wide track gauge. On2 is the smallest of the four NMRA 1/4" O scale track gauges at 1/2".
Now that you know the difference between the UK standard and the NMRA standard, On30 versus On2, you can be confident that the O scale train you select will be the right one for you.
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