O gauge had its heyday when model railroads were considered toys, with more emphasis placed on cost, durability, and the ability to be easily handled and operated by pre-adult hands than on detail and realism.

The original name for O gauge was 0 gauge or Gauge 0, because it was smaller than Gauge 1. At the time, it was believed to be impossible to make a toy train any smaller. Manufacturers such as Ives, American Flyer, and Lionel Corporation used O gauge for their budget line, marketing Wide gauge (also known as standard gauge) as their premium trains. The Great Depression wiped out demand for expensive wide gauge trains, and by 1932, O gauge was the standard, almost by default.

Because of the emphasis on toys, the scale of pre-World War II O gauge trains varied. The Märklin specifications called for 1:43 scale. However, many designs were 1:48 scale, or even 1:64 scale, all while running on the same track. Designers cared more about durability and making the cars look good, rather than accurate. Pre-war locomotives and cars tend to be smaller than post-war equipment.

In the United States in the 1950s, Lionel and Louis Marx and Company sold millions of O gauge toy trains, some of which are now considered collector's items. Both companies struggled in the 1960s, and by the end of the decade, HO scale had overtaken it in popularity.

Since the early 1990s, O scale manufacturers have begun placing more emphasis on realism, and the scale has experienced a resurgence in popularity, although it remains less popular than HO or N scale.

Table of contents

1 O in the United States 2 British and European O gauge 3 O in the Soviet Union

O in the United States

In the United States, O scale is defined as 1:48 (0.25 inches to the foot, "quarter scale"). This is also a common dollhouse scale, giving more options for buildings, figures, and accessories. Many O scale layouts are also accessorized with 1:43 scale model cars.

While 1:48 is a very convenient scale for modeling using the Imperial system (a quarter-inch equals one scale foot), the discrepancy between O scale in the United States and in Europe is attributed to Lionel misreading the original Märklin specifications.

Much equipment in O scale, especially toy trains and the track, are not accurately scaled; a US variant called O27 runs on the same track but (in order to negotiate sharper curves) the locomotives and railroad cars are reduced in length, being approximately 1:64. O gauge track is not true to scale; besides being the incorrect width and possessing a third rail, its height is more than one scale foot. For this reason, O gauge track is sometimes called 'high rail'. This standard survived mostly because of the popularity of Lionel toy trains and the desire for compatibility with Lionel equipment.

However, besides the original three-rail Lionel standard using alternating current, another newer standard exists. Two-rail O scale uses the two running rails as conductors for direct current electricity. While normally the use of scale or gauge is equivalent, O gauge tends to more often mean semi-scale three-rail toy trains, while O scale carries the connotation of two-rail equipment, because of its greater "scale" accuracy, though standard two-rail trains still have an inaccurate gauge, track and wheel profiles.

Dissatisfaction with these standards led to a more accurate standard for wheels and track, called Proto:48. This duplicates to exact scale the AAR track and wheel standards.

Possibly because of the large size of American railroad systems, accurate scale modelling in standard gauge O scale is rare in the US, though narrow gauge modelling in exact-scale On3 (1:48 scale modelling of 3 foot gauge prototypes) or On2 (2 foot gauge prototypes) is much more common.

Although Lionel is the most enduring brand of O scale trains, a variety of manufacturers made trains in this scale. Prior to World War II, shorter-lived companies such as Dorfan, Hafner, Ives, and Joy Line competed with Lionel, Marx, and American Flyer. Many of these pre-war trains operated by clockwork or battery power and were made of lithographed tin. Dorfan went out of business in 1934, while Ives was bought by Lionel, and Hafner and Joy Line were bought by Marx.

Between 1946 and 1976, the primary manufacturers of O gauge trains in the United States were Lionel and Marx, with American Flyer switching to the more-realistic S scale and the rest of the companies out of business. Toy maker Unique Art produced a line of inexpensive O-gauge trains from 1949 to 1951, but found itself unable to compete with Marx. Marx continued to make clockwork and battery-powered trains and lithographed cars into the 1970s, along with more realistic offerings that were sometimes difficult to distinguish from Lionel.

From O scale's beginnings up until the mid-1970s, the various manufacturers' trackside accessories would interoperate with one another, but the train cars themselves used couplers of differing designs, often making it difficult or impossible to use different manufacturers' cars together. The post-War consolidation did little to improve matters: Marx used three different standards, depending on the product line, and Lionel used two, so frequently the companies' own entry-level products were incompatible with their high-end products, let alone with the competition. Hobbyists who wanted differing standards to interoperate had to resort to replacing couplers.

After Marx went out of business in 1978, K-Line bought much of Marx's tooling and entered the marketplace. Little was changed from the old Marx designs besides the brand name and a Lionel-compatible coupler, which made the K-Line offerings completely interoperable with Lionel.

As O gauge regained popularity in the 1990s it also started to regain manufacturers, and as of late 2003, no fewer than six companies market O scale locomotives and/or cars, all theoretically interoperable with one another.

British and European O gauge

In Britain, O gauge equipment is produced at a scale of 1:43, which is 7mm to the foot (using the common British practice of modelling in metric prototypes originally produced using Imperial measurements). It's often called 7mm scale for this reason.

Although toy trains were historically produced to this scale, few to none are still produced even for the collector market (unlike the United States). Modelling in O gauge in fact almost died out in Britain but enjoyed a resurgence in the 1990s as modellers developed a new appreciation for the level of accurate detailing possible in this scale. Few ready to run models are produced in this scale; most are available only as kits for assembly by the modeller or a professional model-builder. O gauge is considered an expensive scale to model in, although the necessarily smaller scope of a larger-scaled layout mitigates this to some extent.

A similar situation exists in Europe, although the market revolves less around kits and more around expensive handbuilt metal models for the deep-pocketed collector.

A finescale version of British 7mm O gauge exists, called ScaleSeven (S7).

O in the Soviet Union

Between 1951 and 1969, a limited number of O gauge train sets were manufactured in the Soviet Union. Utilizing the same track and voltage as their U.S. counterparts, the colorful locomotives and cars superficially resembled pre-World War II designs from U.S. manufacturers--especially Lionel--and the couplers were nearly identical to those of pre-war American Flyer. Some differences in U.S. and Soviet railroading were evident from comparing the Soviet sets with U.S. sets, particularly in the design of the boxcar.