Editing O scale (section)

==Standards==
The differences in the various O gauge and O scale standards can be confusing. O gauge model railroad tracks typically have their rails spaced {{track gauge|1.25 in|lk=on}} apart<ref name="What is O Gauge">{{cite web
 |title        = What is 0 Gauge?
 |url          = http://www.gauge0guild.com/Whatis.asp
 |author       = Ian Middleditch
 |publisher    = Gauge '0' Guild
 |access-date  = 2010-04-11
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20100111220851/http://www.gauge0guild.com/whatis.asp
 |archive-date = 2010-01-11
}}</ref> with the United States [[National Model Railroad Association|National Model Railroad Association (NMRA)]] standard allowing spacings between 31.75&nbsp;mm and 32.64&nbsp;mm.<ref name="NMRA S-1.2 2009.07">{{cite web
 |url          = http://www.nmra.org/standards/sandrp/pdf/S-1.2%202009.07.pdf
 |title        = NMRA STANDARDS S-1.2 Standards for Scale Models
 |date         = July 2009
 |access-date  = 2010-04-11
 |publisher    = [[National Model Railroad Association]]
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20100706185702/http://www.nmra.org/standards/sandrp/pdf/S-1.2%202009.07.pdf
 |archive-date = 2010-07-06
}}</ref>

===Scale and gauge===
[[Scale (ratio)|Scale]] refers to the size of the model relative to the actual full-sized object being represented, while [[Rail gauge|gauge]] is the width of the model track. Most commercially produced model track is a compromise between appearance and a trouble-free running surface.

====Scale====
Scale is the ratio of a model dimension to the real life dimension. O Scale in the UK is commonly 1:43.5 or 7&nbsp;mm to the foot. In continental Europe it is commonly 1:45. 1:43.5 is also used, particularly in France.<ref name="NEM-010">{{cite web|url=http://www.morop.org/fr/normes/nem010_f.pdf|title=Normes Européennes de Modélisme: Rapports de réduction, échelles, écartements|year=2004|publisher=Union Européenne des Modélistes Ferroviaires et des Amis des Chemins de Fer|language=FR|access-date=2010-04-11}}</ref> In the USA, 1:48 is common.<ref name="NMRA S-1.2 2009.07"/> The [[National Model Railroad Association|NMRA]] and the [[MOROP]] maintain detailed standards for a variety of scales to help model makers create interoperable models.<ref name="NEM-010"/><ref name="NMRA Intro">{{cite web
 |url          = http://www.nmra.org/standards/standards.html
 |title        = Standards & Recommended Practices - Introduction
 |date         = 2008-02-17
 |author       = T.J. Klevar
 |access-date  = 2010-04-11
 |publisher    = [[National Model Railroad Association]]
 |url-status   = dead
 |archive-url  = https://web.archive.org/web/20100403082408/http://www.nmra.org/standards/standards.html
 |archive-date = 2010-04-03
}}</ref>

====Gauge====
''Gauge'' refers to the distance between the inside edges of the load-bearing rails. Various sizes of [[track gauge]] exist around the world and the normal O gauge track represents the [[Standard gauge]] of {{Track gauge|1435 mm}}. "O gauge" refers to tracks that are nominal {{Track gauge|32mm}} according to older standards of NMRA, current standards of BRMSB and NEM. {{Track gauge|1.25 in}} apart current standards of NMRA.<ref name="What is O Gauge"/> When used as a [[narrow-gauge]] track, O gauge allows scales such as 1:32 representing {{Track gauge|1000 mm}} gauge track. 1:20 representing {{Track gauge|600 mm}} [[narrow-gauge railway]]s.

Regional model manufacturers design their O-scale rolling stock with minor regional scale differences—manufacturers support their rolling stock with track made to the same regional scales, so there is no universal width for O-gauge model track.{{Citation needed|date=April 2010}} Models could represent the real-world standard gauge track spacing of {{Track gauge|1435 mm|disp=1}} by choosing various spacings such as {{Track gauge|30 mm}} at 1:48 scale, {{Track gauge|1.25 in}} at 1:45.2 scale, {{Track gauge|32 mm}} at 1:44.8 scale, {{Track gauge|32.96 mm}} at 7&nbsp;mm:1&nbsp;ft scale, and {{Track gauge|33 mm}} at 1:43.5 scale. Model makers choose their scale based on many considerations including the existing marketplace, aesthetic concerns and compatibility with existing models.

====Wide- or narrow-gauge track====
[[File:Spur 0e Zahnradbahn im Modelleisenbahnclub Basel mit He 2 2 und Vorstellwagen 2021.jpg|thumb|Probably the oldest known 0e gauge vehicles in the MCB from 1947. WAB rack railway train, 2021]]
Some O-scale modelers choose to model prototypes at other than standard gauge and follow wide gauge (also known as [[broad-gauge]]) or [[narrow-gauge]] railroads. There is no standard for wide- or narrow-gauge model track, and modelers wishing to portray such railway track either build their own, or more commonly accept the shortcomings of appropriately wider or narrower gauge model track. {{Track gauge|16.5mm}}, {{Track gauge|12mm}} and {{Track gauge|9mm}} are the more popular track widths used by indoor enthusiasts modeling narrow gauge. Differences in regional scales give different prototype gauges to these different model track widths.

For example, using specially manufactured {{Track gauge|16.5mm}} gauge track, scaled at 7&nbsp;mm to the foot (with appropriately spaced, larger [[Railroad tie|sleepers]], etc.) underneath:
# UK O scale rolling stock (1:43.5), it becomes a narrow-gauge track of {{Track gauge|2ft4in}}, and is referred to as "[[On30 gauge|O&nbsp;16.5]]". Modelers portray gauges between {{Track gauge|2ft}} and {{Track gauge|3ft}}.
# European O scale rolling stock (1:45 or 1:43.5 in France), it becomes a narrow-gauge track of {{Track gauge|750mm}}, and is referred to as "[[Oe gauge|Oe]]" portraying a {{Track gauge|750mm|disp=1}}, {{Track gauge|760mm|disp=1}} and {{Track gauge|800mm|disp=1}} prototype. Modelers portray gauges between 650 mm and 800 mm prototype.
# United States O scale rolling stock (1:48), it becomes a narrow-gauge track of {{Track gauge|2ft6in}}, and is referred to as "[[On30 gauge|On&nbsp;2½]]" (or On30, as in 30 inches).

===Om gauge===
[[File:FAMA-Alpenbahn Lang Spur 0m 0-22,5 RhB Ge 6 6 704 Davos rot.jpg|thumb|Om gauge (O-22.5 gauge), model of the RhB Ge 6/6 II 704 in 1:45 scale from parts of the former FAMA-Alpenbahn and Lang Modellbau, 2019]]

[[File:Modelleisenbahn Diorama nach Vorbild der Sernftalbahn mit SeTB BCFe 2 2 4 Spur 0m Spur 0-22,2 2021.jpg |thumb|Om gauge (O-22.2 gauge), Diorama based on the SeTB with a selfmade motor coach of the type BCFe 2/2 4, 2021]]

The Om gauge (O-22.5 gauge) includes the actual narrow-gauges from 850 to 1250 mm and with it the [[metre-gauge railway|metric gauge]]. This applies to both 1:43.4 and 1:45 scale model trains. Metric model railroaders generally use the 0m scale with a gauge of 22.5 mm. The starting point is the NEM standards concerning 0m gauge that were created at the end of the 1950s.

===O-27 gauge===
''O-27 gauge'' is variant whose origins are slightly unclear. Some historians attribute its creation to [[A. C. Gilbert Company]]'s [[American Flyer]], but [[Ives Manufacturing Company]] used O-27 track in its entry-level sets at least a decade before Gilbert bought Flyer.

The modern standard for O-27, however, was formalized after 1938 by Gilbert, who scaled the locomotives and rolling stock to [[1:64 scale]]. After World War II, this practice was continued by [[Louis Marx and Company]], who used it throughout its product line, and [[Lionel, LLC|Lionel]], who used it for its entry-level trains. O-27 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. A shim underneath the O-27 track enables the use of O and O-27 track together.

The O-27 name comes from the size of the track's curves. A circle made of eight pieces of standard 45-degree curved O gauge track will have a {{convert|31|in|mm|sigfig=3}} diameter. A circle made of 8 pieces of 45-degree curved O-27 track is smaller, with a {{convert|27|in|mm|sigfig=3}} diameter. Full-sized O cars sometimes have difficulty negotiating the tighter curves of an O-27 layout.

Although the smaller, tin lithographed cars by American Flyer, Marx, and others predate the formal O-27 standard, they are also often called O-27, because they also operate flawlessly on O-27 track. Marx may have dedicated its entire line to O-27, but only the [[Lionel Corporation]] remains to produce O-27 track and trains. Its tubular rail is a standard of the tinplate era.

===Super-O gauge===
"Super-O gauge" is a variant whose origin stems from Lionel's desire to create a more realistic looking track and improve sagging sales in the late 1950s.{{Citation needed|date=March 2022}}

===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 [[Association of American Railroads|AAR]] track and [[wheel]] standards.<ref>{{cite web |title=The History of Proto48 |url=http://www.proto48.org/p48_information.htm |work=Proto48 Modeler |access-date=22 September 2013}}</ref> In the United Kingdom a similar [[ScaleSeven]] system exists.

The track gauge normally used for O of 32&nbsp;mm or the near-approximation {{frac|1|1|4}}&nbsp;inch is for [[Standard gauge]] ({{Track gauge|1435mm}}) approximately equivalent to {{Track gauge|5ft}} at 1:48 scale, {{Track gauge|4ft8.5in}} at 1:45 and {{Track gauge|4ft6.5in}} at 1:43.5.<ref name=Hollingsworth>{{cite book |last=Hollingsworth |first=Brian |title=Model Railroads|year=1981 |publisher=Bison Books |location=London, UK |isbn=0-60034944-6}}</ref>

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

Four common narrow-gauge standards exist, and the differences among ''On3,'' ''On2,'' ''On30,'' and ''On18'' are frequent sources of confusion. On3 is exact-scale 1:48 modeling of {{Track gauge|3ft}} gauge prototypes, while [[On30]] is [[1:48]] modeling of {{Track gauge|2ft6in}} gauge prototypes, On2 is 1:48 modeling of {{Track gauge|2ft}} gauge prototypes, and On18 is 1:48 modeling of {{Track gauge|18in}} gauge prototypes. On30 is also sometimes called On2½.

Because On30's gauge closely matches that of HO track, On30 equipment typically runs on standard HO scale track. While many On30 modelers [[Scratch building|scratchbuild]] their equipment, commercial offerings in On30 are fairly common and sometimes very inexpensive, with [[Bachmann Industries]] being the most commonly found manufacturer.

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

===Power supply===
Models that are either built to [[1:43 scale]], 7&nbsp;mm:1&nbsp;foot (1:43.5), 1:45 scale, or [[1:48 scale]] can run on realistic-looking two-rail track using [[direct current]] (Commonly known as ''2-Rail O''), or on a center [[third rail (model railroading)|third power rail]] or a center stud supply system. If modeling such a system, an external third rail or overhead supply may be employed.

While two-rail O has traditionally been more popular in Europe, and [[alternating current]] powered three-rail more popular in the United States, two-rail O is currently experiencing a resurgence in popularity in the United States, due to increased availability of ready-to-run models from several manufacturers. The recent development of Digital Command Control (DCC) power systems with built in sound have also increased the popularity of two rail O scale models.

===Die-cast metal models compatible with O scale===
Many manufacturers produce [[die-cast models]] of trucks, cars, buses, construction equipment and other vehicles in scales compatible with or similar to O scale model trains. These are available in [[1:43 scale]], [[1:48 scale]] and [[1:50 scale]]. Manufacturers include [[Conrad (company)|Conrad]], NZG, [[Corgi Toys|Corgi]], [[TWH Collectibles]]. [[Ertl Company|Ertl]], and many others. These are popular with collectors and easy to find.