HO scale

German and U.S. HO scale trains and buildings on 18" wide shelf

German HO scale trams and bus

This center cab switch engine is a GE 44-ton diesil locomotive made by Bachmann Industries.

HO scale (H0 scale in continental Europe) is the most popular scale of model railway in most of the world (outside the United Kingdom, where the slightly larger in scale OO scale is most common). The name is derived from the German Halb-null ("half-zero"), because its 1:87 scale is approximately half that of O scale.

In HO scale, 3.5 millimetres represents 1 real foot; this awkward ratio works out to about 1:87.086. In HO, rails are usually spaced 16.5 millimeters apart which models the standard railroad gauge of 4' 8.5".

Modern HO trains run on realistic-looking two-rail track, which is powered by direct current (varying the voltage applied to the rails to change the speed, and polarity to change direction), or by Digital Command Control (sending commands to a decoder in each locomotive). Some trains, most notably by Märklin of Germany, run on alternating current, supplied by a "third rail" consisting of small bumps on each tie down the centre of the track.

History

HO scale trains first appeared in the United Kingdom in the 1930s, originally as an alternative to OO scale. It proved unsuitable for scale modelling UK trains. However, it became very popular in the United States, where it took off in the late 1950s after interest in model railroads as toys began to decline and more emphasis began to be placed on realism in response to hobbyist demand. While HO scale is by nature more delicate than O scale, its smaller size allows modelers to fit more details and more scale miles into a comparable area.

In the 1960s, as HO scale began to overtake O scale in popularity, even the stalwarts of other sizes, including Gilbert (makers of American Flyer) and Lionel Corporation began manufacturing HO trains. HO locomotives, rolling stock (cars or carriages), buildings, and scenery are available today from a large number of manufacturers in a variety of price brackets.

Variations

HO scale has several narrower gauges to represent narrow gauge trains in the same scale as their HO counterparts, these include:
- HOe scale - with 9 mm gauge tracks (the same as N scale), usually used to represent 2 foot gauge in HO Scale.
- HOm scale - with 12 mm gauge tracks (the same as TT scale), usually used to represent meter gauge in HO Scale; this is a particularly popular scale in Europe.
- HOn3 - used to represent 36" gauge in HO Scale.
- HOn30 - used to represent 30" gauge in HO Scale (also known as HOn2½).
- HOz - using 6.5mm (Z gauge) track to represent the 15" gauge as used in parks and some garden railways.


In addition, the term HO, when used in the hobby of slot car racing, does not denote a precise scale, but a general size of track on which the cars can range from 1:87 to approximately 1:64 scale.