Scale for Locomotives/ Rolling stock, includes Track gauges, and rail codes.

Prototype: - An original full size item.
Scale modeling: - Miniaturization of an original full size item to a desired scale.
S Scale: - 1/64th or (3/16" = 1') reduction in size of the prototype (proto).
S Gauge: - Track width, inside edge to inside edge of rail heads, .883-.905, AKA 7/8".
Rail code: - Height of rail in thousandths.

Scale and Gauge! Scale being the reduction in size of the prototype of everything on your layout when modeling to a desired scale (miniaturization). However, gauge is the established width between rails of prototype or modeled track. To establish track gauge, measure perpendicularly across the inside edges of the railheads. Track height and weight vary in prototype and modeled track as to the main line, yard, branch and spurs. In order to effectively compliment track realism, modeling vendors have specialty track, turnouts and crossovers for this purpose.

Model railroad type example Sn3.5 is as follows, S (scale) being the prefix to n (narrow gauge) followed by 3.5 (prototype track gauge in feet), 3 and 1/2 feet, or 42 inches, which in Sn3.5 equates to actual modeling track width of .649 - .672 thousandths, 16.5 - 17.1 mm. Track gauge specifications including rail height codes, see table below.

Guidelines for "S and Sn model railroading mechanics". The scale of everything in the layout including locomotive and rolling stock body shells, wheel diameters etc, are S scale, being 1/64th prototype whenever possible. The functioning mechanical equipment in contact with the rails as to gauge shall be sized to match the intended track gauge, again measuring inside edge to inside edge of rails, use rail height codes and set coupler heights as required.

Sn locomotives and rolling stock may be bought, built or modified. Selecting modify may require sizing locomotives, rolling stock body shells, driven wheels, trucks, and couplers (bashing) to compliment your desired period and gauge.

Difference in S and Sn? Mid to late 1800s narrow gauge locomotives are small when compared to 1950s standard gauge locomotives, the track gauge for narrow gauge prototype locomotives generally measured from 24" to 42", where the standard gauge for the larger style 1950s prototype locomotives would have been 56 -1/2", therefore, differences in S and Sn varieties are generally variations specific to track height, rail weight, gauge and couplers.

Narrow gauge modelers gravitate to the 19th and early 20th century American layouts to create for themselves historically correct prospectives as to the period they present, while modeling to a museum quality standard.

Sn4 is presented as a non-purist model railroad. Locomotives and rolling stock are S standard with functioning mechanical equipment sized to operate on the narrower On3 track while utilizing On3 trucks and couplers.

Type and Scale Track Gauge Specifics Available Rail Code Heights
S Standard
S Narrow		 Scale
(3)		 Track
Scale		 Track
Guage		 Min/Max
Inches		 Min/Max
mm		 Guage
AKA		 Proto
Guage
S 1/64 1/64 S .884 - .905 22.4 – 23.99 7/8" 56.5" .070 .083 .100 .125 .148 .220
Sn4 1/64 1/76 On3 .750 - .772 19.1 – 19.8 3/4" 48" .070 .083 .100
Sn4* 1/64 1/76 OO .750 - .772 19.1 – 19.8 3/4" 48" .070 .083 .100
Sn3.5 1/64 1/87 HO .649 - .672 16.5 – 17.1 5/8" 42" .055 .070 .080 .083 .100
Sn3.5* 1/64 1/87 On30 .649 - .672 16.5 – 17.1 5/8" 42" .055 .070 .080 .083 .100
Sn3 1/64 1/100 Sn3 .563 - .586 14.3 – 14.9 9/16" 36" .040 .055 .070 .083 .100
Sn3* 1/64 1/100 OOC .563 - .586 14.3 – 14.9 9/16" 36" .040 .055 .070 .083 .100
Sn2.5 (1) 1/64 1/114 On2 .500 - .522 12.7 – 13.3 1/2" 30" .040 .055 .070 .083
Sn2.5 (2) 1/64 1/120 TT .471 - .483 12.0 – 12.3 12mm 30" .040 .055 .070 .083
Sn2 (1) 1/64 1/140 HOn3 .413 - .424 10.5 – 10.77 13/32" 24" .040 .055 .070 .083
Sn2 (2) 1/64 1/160 N .353 - .367 8.97 –  9.32 9mm 24" .040 .055 .070 .083
(1) Wide track version.   (2) Narrow track version.   (3) Locomotives and rolling stock.   * gauge equivlent.   Hi-Rail Scale (Red).   Hi-Rail Tinplate (Green).


To those of you, who are just entering S scale, "Welcome to the neighborhood".


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