Editing O scale (section)

===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.