Z gauge (or Z scale) is the smallest (1:220) model railway scale. Its micro track scale measures only 6.5 mm. Z gauge was introduced by Märklin, a German model railway manufacturer in 1972 at the Nuremberg Toy Fair. It was invented by Märklin's head design engineer Helmut Killian. Letter Z was chosen to designate the new gauge as it was thought at the time that there would not be a commercial model railway scale even smaller than Z, in the future. Hence the last character of the alphabet in German & English languages.
These Z scale trains operate on 8-10 volt DC and offer the same operating characteristics as all other two-track, direct-current, analog model railways.
In 1978 a Märklin Z scale locomotive pulling six coaches made its entry to Guinness Book of Records by running nonstop 1219 hours and travelling a distance of 720 km before the train stopped.
The extremely diminutive size of Z scale makes it possible to build very compact train layouts that can easily fit a normal size briefcase. Z scale can also be beneficial when there is a need to fit more scale space into the same physical layout that would be used by a larger-scale model. Several transportation museums, for instance, have used Z scale to present some real world railway sceneries in smaller scale. Theoretically Z scale allows longer trains and smoother curves, and more realistic operation than is possible in larger scales.
However, due to the extreme size of Z scale, and the reduced weight of the locomotives (a small Z scale engine can weigh as little as 20 grams, well under one ounce), it can be challenging to assure reliable operation of a layout. In particular, the track must be kept clean - spots of dirt or oxidized track can stop the locomotive instantly. Poorly installed trackwork can be a source of constant derailings of rolling stock. The low weight of Z scale locomotives contributes also to their difficulty to pull trains uphill and in practice the grade should be kept rather moderate. For trains of reasonable length (six four-axle cars) 2% grade is about the maximum for reliable operation. For shorter trains it is possible to go up to 4%.
Pulling power of locomotives can be increased by adding weight inside, but due to the limited space available, it is vital that the substance chosen has a relatively high density. Tungsten powder and lead are popular choices among Z scale enthusiasts for this purpose. Some recent Z scale locomotives are also built in a somewhat heavier style, which shows as an improved pulling capacity.
While Märklin remains still the most important Z scale rolling stock manufacturer, there are smaller manufacturers of Z scale rolling stock both in Europe and in North America targeting some niche areas of Z scale demand. For instance, the German company Freudenreich Feinwerktechnik has introduced a complete narrow-gauge z-scale system with only 4.5mm gauge track which corresponds to metric gauge in prototype and is designated as Zm scale following the NEM standard scale naming system.
Z scale is predominantly European scale, but it has an increasing number of loyal followers in other parts of the world too. Z scale enthusiasts throughout Europe and North America participate regularly at most national and regional model railroad exhibitions and shows, where they have demonstrated the outstanding operational and layout design characteristics of the scale.
As early as 1988, Märklin announced their intention to offer digital train control systems in Z scale and Märklin's 1988 Z scale product catalog listed three locomotives with a built-in digital decoder. Unfortunately, the technology was not developed enough and the manufacturer had to cancel these plans mainly due to heat dissipation problems of locomotive decoders. Since then, these problems have been solved, and Z scale has embraced advanced electronics. An increasing number of modellers have converted their locomotives to use third party digital train control systems. Popular systems are the European standard Selectrix, which offers some of the smallest decoders with thicknesses of less than 2 mm, and also the universally popular Digital Command Control (DCC).
Today Z scale, while still considered to be a curiosity by some, is a legitimate, mature, modelling scale. However, Z scale rolling stock, buildings and figures remain still somewhat less widespread and higher priced than their counterparts in more popular HO scale, OO scale, and N scale.