N scale is a popular model railway size. Depending upon the manufacturer, the scale ranges from 1:148 to 1:160. In all cases, the gauge (the distance between the rails) is 9 mm. The term N gauge refers to the track dimensions, and is not a scale. Nevertheless, the terms N scale and N gauge are often used interchangeably. An advantage of N scale is that it allows hobbyists to build layouts that take up less space than HO scale, or put longer track runs into the same amount of space, because the models are smaller (by nearly a half) than they are in HO scale (1:87). The name comes from an abbreviation for Nine millimetres, which is the distance between the inside edges of the rails.
In Britain, some N scale models are built to "2 mm scale" for "2 mm to the foot" which calculates to a 1:152 proportion. Early N scale was also known as "OOO" or "Treble-O" in reference to O and 00 and was also 1:152, though for an entirely different reason.
In the United States and Europe, models of standard gauge (4ft 8.5in) trains are built to 1:160 scale and made so that they run on N gauge track. In the United Kingdom a scale of 1:148 is used for commercially produced models. In Japan, a scale of 1:150 is used for the models of 3 ft 6 in gauge trains, while a scale of 1:160 is used for models of standard gauge Shinkansen (Bullet Train) models. In the U.S. and Europe, a scale of 1:160 is used for models of trains, irrespective of the gauge of the real trains they are scaled from. All of these scales run on the same 9mm track gauge (N gauge). This means the track is a little too narrow for 1:148/1:150 but the difference is usually considered too small to matter. Strict 2mm fine scale modellers use slightly wider and usually hand built track.
Although trains and accessories of similar gauge and/or scale existed as early as 1927, modern N scale only appeared in 1962. Unlike other scales and gauges, which were de facto standards at best, within two years N scale manufacturers defined the gauge, voltage, as well as the height and type of couplers.
N scale locomotives are powered by DC motors which accept a nominal maximum of 12 V DC. In traditional DC control, the speed of the train is determined by the amount of voltage supplied to the rails. The direction of the train is determined by the polarity of the power to the rails. Since the end of the 20th century, an increasing number of enthuisiasts have started using Digital Command Control (DCC) to determine the speed and direction of their trains. This has in part been made possible by surface mount technology and new motors that draw very little current (typically 0.2amps).
The agreed-to standard coupling is known as a 'Rapido' coupler from the manufacturer (Arnold). Most companies developed their own variants of this coupler to avoid Arnold patents on the spring system. Graham Farish initially adopted a plastic flexible U rather than a spring, Peco used a compatible weighted coupler system (Elsie) and Fleischmann cunningly sidestepped the problem by using a sprung plate. All however were compatible.
The Rapido coupler system works well but is difficult to use for automatic uncoupling and also relatively large. U.S. and Canadian modellers are making more and more use of a more realistic looking proprietary coupler system, available from Micro-Trains Line Co.. The MT couplers (as they are known) are more delicate and closer to scale North American appearance than Rapido couplers. Other manufacturers are now making couplers that mate with Micro Trains couplers although without all the features of the MT couplers due to MTL owned patent rights.
European modellers have the option to convert the couplings on their rolling stock to the Fleischmann Profi-Coupler system for more reliable operation should they wish to do so, but most N scale rolling stock continues to be manufactured with Rapido couplers - a design which is fairly robust and easy to mold. Modern N scale stock uses a standard NEM socket for couplers which allows different coupling designs to be used by simply pulling out the old coupler and fitting a new one of a different design.
N scale has a large worldwide following. Models are made of very many standard gauge prototypes from every continent. N scale's popularity is second only to HO scale's. In Japan, where space in homes is more limited, N scale is the most popular scale, and HO scale is considered large. Not all modellers select N because they have small spaces, some use N scale in order to build more complex or more visually expansive models.
N gauge track and components are also used with larger scales, in particular HOe and 009 scale for modelling narrow gauge railways. N scale models on Z scale track are used to model metre gauge (Nn3). A small amount of 2' indusrial narrow gauge modelling in N scale using custom track is done but there are few suppliers of parts.