O scale

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O scale (or O gauge) is a scale commonly used for toy trains and model railroading. Originally introduced by German toy manufacturer Märklin around 1900, by the 1930s three-rail alternating current O gauge was the most common model railroad scale in the United States and remained so until the early 1960s. In Europe, its popularity declined before World War II due to the introduction of smaller scales.

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. Detail and realism were secondary concerns, at best.

O gauge remains a popular choice for hobbyists who enjoy running trains more than they enjoy other aspects of modeling, and collecting vintage O gauge trains is also popular. In addition, a number of changes in recent years have addressed the concerns of scale model railroaders, making O scale more popular, at least in the United States.



The original name for O gauge and O scale was 0 [zero] gauge or Gauge 0, because it was smaller than Gauge 1 and the other existing standards. At the time, it was believed to be impossible to make a toy train any smaller. It was created in part because manufacturers realized their best-selling trains were the smaller scales.

In the United States, manufacturers such as the Ives Manufacturing Company, American Flyer, and Lionel Corporation used O gauge for their budget line, marketing either Gauge 1 or Wide gauge (also known as standard gauge) as their premium trains. The Great Depression wiped out demand for the expensive larger trains, and by 1932, O gauge was the standard, almost by default.

Because of the emphasis on play value, 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 1:64 scale. Entry-level trains, usually made of lithographed tinplate, were not scaled at all, made to whimsical proportions about the same length of an HO scale piece, but about the same width and height of an O scale piece. Yet all of these designs ran on the same track, and, depending on the manufacturer(s) of the cars, could sometimes be coupled together and run as part of the same train.

After World War II, manufacturers started paying more attention to scale, and post-war locomotives and rolling stock tend to be larger and more realistic than their earlier counterparts.

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.


The differences in the various O gauge and O scale standards often confuse newcomers.

O gauge and O scale

O scale tends to imply an accurate scale model at 1:43, 1:45, or 1:48 scale. It may run on traditional three-rail track, but more likely, it runs on more realistic-looking two-rail track using direct current. However, the height and spacing of the rails is not true to scale. Often, hobbyists will use the phrases "two-rail" or "three-rail" to clarify which they mean.

To some O gauge usually implies a toy train running on three-rail track, scaled at approximately 1:48. To many it is a gauge which allows larger precision models to be made to. Using the odd scale of 7mm = 12 inches a scale of 1/43.5 is established. Especially in the UK many models are made to this scale for running on layouts, small and large, indoors and out.

When used as a narrow gauge track 0 gauge allows scales of 1/32 representing 40" or meter gauge track. 1/20 representing 24"/600mm narrow gauge railways.

However, the two phrases are often also used interchangeably, particularly on eBay.

O27 gauge

O27 gauge is a variant whose origins are slightly unclear. Some historians attribute its creation to A. C. Gilbert Company's American Flyer, but Ives used O27 track in its entry-level sets at least a decade before Gilbert bought Flyer.

The modern standard for O27, however, was formalized after 1938 by Gilbert, who scaled the locomotives and rolling stock at 3/16 inches to the foot, or 1:64. After World War II, this practice was continued by Louis Marx and Company, who used it throughout its product line, and Lionel, who used it for its entry-level trains. O27 track is spaced at the same width as regular O gauge track, but is slightly shorter in height and has thinner rails than traditional O gauge track. For these reasons, regular O and O27 track cannot be used together without difficulty.

The name comes from the size of the track's curves. A circle made of eight pieces of standard curved O gauge track will have a 31 inch (787 mm) radius. A circle made of 8 pieces of curved O27 track is smaller, with a 27 inch (686 mm) radius. Full-sized O cars sometimes have difficulty negotiating the tighter curves of an O27 layout. Although the smaller, tin lithographed cars by American Flyer, Marx, and others predate the formal O27 standard, they are also often called O27 because they also operate flawlessly on O27 track.

The O27 standard is still used today by Lionel, K-Line, and others for its least expensive O gauge trains. It is most popular with children and with people who have limited space, as it is the least realistic of the O scale standards.

Exact scale standards

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.

The track gauge normally used for O is correct for British O but not American. The difference between the two also explains why HO is 1:87 - it is 3.5 mm to the foot, half of British O, but is not used in Britain.

Possibly because of the large size of American railroad systems, accurate scale modeling in standard gauge O scale is rare in the United States, though narrow gauge modeling is much more common.

Four common narrow gauge standards exist, and the difference between On3, On2, On30, and On18 is a frequent source of confusion. On3 is exact-scale 1:48 modeling of 3 foot (914 mm) gauge prototypes, while On30 is 1:48 modeling of 30 inch (762 mm) gauge prototypes, On2 is 1:48 modeling of 2 foot (610 mm) gauge prototypes, and On18 is 1:48 modeling of 18 inch (457 mm) gauge prototypes. On30 is also sometimes called On2½.

Because On30's gauge closely matches that of HO scale, On30 equipment typically runs on standard HO scale track. On30 is considered by many to be the fastest growing segment of the model railroad hobby in general, and while many On30 modelers scratchbuild their equipment, commercial offerings in On30 are fairly common and sometimes very inexpensive, with Bachmann Industries being the most commonly found manufacturer. Bachmann's On30 trains are sometimes sold side by side with the company's HO offerings.

Hobbyists who choose to model in any of these O scale standards nevertheless end up building most, if not all, of their equipment either from kits or from scratch.

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.

Although Lionel is the most enduring brand of O gauge trains, a variety of manufacturers made trains in this gauge. Prior to World War I, the majority of toy trains sold in the United States were German imports made by Märklin, Bing, Fandor, and other companies. World War I brought a halt to these German imports, and protective tariffs after the war made it difficult for them to compete.

In between the two world wars, shorter-lived companies such as Dorfan, Hafner, Ives, and Joy Line competed with Lionel, Louis Marx and Company, American Flyer and Hornby. Many of these pre-war trains operated by clockwork or battery power and were made of lithographed tin. The sizes of the cars varied widely, as the standard for O scale was largely ignored. Dorfan went out of business in 1934, while Ives was bought by Lionel, and Hafner and Joy Line were bought by Marx. Hornby withdrew from the U.S. market in 1930 after selling its U.S. factory to the A. C. Gilbert Company.

As early as 1938, the survivors Lionel, Marx, and American Flyer faced competition from Sakai (also sometimes spelled "Seki"), a Tokyo-based Japanese toy company who sold trains priced at the low end of the market. The product designs most closely resembled Lionel, but with Märklin-like couplers and detail parts that appeared to be copied from Ives.

Between 1946 and 1976, the primary U.S. manufacturers of O gauge trains 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.

Sakai re-entered the U.S. market after World War II, selling trains that were often nearly identical to Marx designs and sometimes undercutting Marx's prices, from 1946 to 1969.

A company called American Model Toys brought out a line of realistic, detailed cars beginning in 1948. In 1953 it released a budget line. It ran into financial difficulty, reorganized under the name Auburn Model Trains, and ended up selling its line to Nashville, Tennessee-based Kusan, a plastics company who continued its production until 1961. The tooling was then sold to a small company run by Andy Kriswaulis in Endicott, New York, who operated as Kris Model Trains, or KMT. After Kriswaulis' death, the tooling was sold to K-Line and Williams Electric Trains, who continued to use it to produce parts of their budget lines.

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. K-Line's early offerings changed little from the old Marx designs, other than a new brand name and a Lionel-compatible coupler, making K-Line's 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.

Lionel equipment retains a large collector following. Equipment from shorter-lived manufacturers prior to World War II is also highly sought after, while American Flyer and Marx are less so. Post-War Marx is gaining in popularity after years of being derided by serious collectors. There is little collector interest in Sakai today, possibly because of difficulty identifying the equipment and because the brand is much less widely known than its U.S. counterparts.

British and European O gauge

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

Although toy trains were historically produced to this scale, O gauge's popularity in Europe and Britain died out after World War II, and the standard is rarer than in the United States. Modeling in O gauge in fact almost died out in Britain but enjoyed a resurgence in the 1990s as modelers 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. The two dominant British manufacturers, Bassett-Lowke and Hornby, ceased production of O gauge trains in 1965 and 1969, respectively. However, Ace Trains and a revived Bassett-Lowke are once again producing tinplate O gauge sets, many of them reproductions of classic Hornby and Bassett-Lowke designs.

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. Additionally, Czech Republic-based Electric Train Systems started manufacturing and selling lithographed tin 1:45 scale trains in 1991, citing O scale's advantages over smaller sizes for non-permanent floor layouts and outdoor layouts. The Spanish company Paya produces a smaller line of tinplate trains, based on designs dating back to 1906.

In Germany a narrow gauge O scale train set is produded by Fleischmann, running on 16.5mm track, this scale is called 0e (750mm prototype). This trains are marketed as children toy trains (Magic Train), but are accurately built after Austrian prototypes and increased the interest in building narrow gauge layouts in O-scale in Germany and Austria significantly.

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

The British 1:43 rail scale gave birth to series of die cast cars and model commercial vehicles of the same scale which gradually grew in popularity and spread to France, the rest of Europe and North America at the same time that the rail models were becoming less popular.

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 resembled pre-World War II designs from U.S. manufacturers Lionel and American Flyer 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, which looked like an American Flyer boxcar with windows added, reflecting the Soviets' use of box cars to haul livestock, as well as merchandise.

Much like their American counterparts, Soviet O gauge trains were toys, rather than precision-scaled models.


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