Although it may be mistakenly called N-Gauge, derived from some of the earliest mass produced 1:152 "OOO" or "Treble-O" scale models manufactured by the British firm, Lone Star, in 1961, 9 mm wide (i.e., a track gauge of 0.354 inches, as measured between the inner sides of the rail) contemporary N-Scale model production was initiated by the German firm, Arnold Rapido, in 1962.
While a rail gauge of 9 mm remains constant for standard gauge (as opposed to narrow gauge) N-Scale locomotives and rolling-stock, depending upon the place of manufacture and/or the specific market that a model is targeted to be sold in, its size in proportion to its prototype (i.e., "scale") may be 1:148 (British), 1:150 (for Japanese 3 foot 6 inch /1,067 mm or 4 foot 6 inch / 1,372 mm gauge trains), or 1:160 (for North American, Japanese 1,435 mm high-speed trains, and European) scale.
Though 9 mm wide track is often used to model narrow gauge lines in larger scales (e.g., HOn2-1/2 or HOe), Z-Scale (6.5 mm/0.256 inch) products are typically used when modeling similar railway systems (Nn3) in N-Scale.
As is the case with prototype railways, N-Scale manufacturers produce rail in different heights.
Expressed in thousandths of an inch, track "Code" refers to the measured height of manufactured model rail. Extremely popular and larger than most prototype rail, code 80 (0.080-inches tall or about 12 scale inches high) has been the industry standard for years.
Typically designed for modelers seeking products that are closer to scale, manufacturers also produce rail in Code 70 (0.070 inches tall or about 11 scale inches high), Code 55 (0.055 inches tall or about 9 scale inches high), and Code 40 (0.040-inches tall or about 6 scale inches high).
While adopting more scale-like rail may initially sound great, there are a three caveats to consider:
1. Older N-Scale models may need to have their wheels and/or wheel-sets modified or replaced due to the height of the factory-supplied wheel flanges, which will often hit the top of the simulated spike heads that secure the low profile rails to their ties or sleepers. Retrofitting rolling-stock with aftermarket low-profile wheel-sets is fairly easy, and can usually be done at moderate cost
2. Though the tolerances of wheels and wheel-sets should be checked before newly acquired models are initially run, closer attention must be paid to wheel gauge and flange heights whenever low-profile rail is utilized.
3. With regards to North American style N-Scale track, there is presently a somewhat limited range of prefabricated products available in anything other than Code 80.