The NASG maintains the track and wheel standards for the S-scale community. This page lists the latest accepted standards. Standards are maintained so that equipment from various manufacturers can run on track from various manufacturers. If you hand-lay track to these standards, the equipment made to these standards will run on your track.
Throughout this web site we refer to modeling in 1:64th scale as "S-scale" (the hyphen is significant). You will find magazines and other web sites using the term "S-gauge" or "S gauge". That terminology is not correct, but it has its roots in when the model railroading hobby started many decades ago.
You will find similar terminology used in other scales as well (e.g. "N gauge"). The word "gauge" refers to the distance between the rails, while "scale" is the ratio of prototype (real-world) size to the modeled size. We have "standard-gauge" (4'8-1/2" of spacing between the rails) and "narrow-gauge" (e.g. 3 feet between the rails), yet locomotives that run on these rails are both scaled to 1/64th of the real thing.
Due to S-scale's history being tied to American Flyer, there is further confusion in that, within the S-scale community, there are sub-divisions, such as American Flyer, hi-rail, scale, narrow-gauge, etc. Some refer to "S gauge" as meaning either American Flyer and/or hi-rail, and "S scale" as being scale modeling (standard-gauge or narrow-gauge). This is incorrect, because all models are still 1/64th of the real thing, so all are indeed S-scale.
If the distinction needs to be made between "American Flyer", "hi-rail", or "scale" modeling, it will be so indicated on this site using those words as shown in these quotes. The NMRA standard uses the term "deep-flange", which would apply to S-scale's American Flyer and most hi-rail modeling.
Within S-scale, the difference between all of these sub-divisions really only boils down to whether or not your equipment uses deep flanges and/or A.F.-compatible claw couplers vs. more scale-like couplers. Other distinctions, such as level of detail on the models, and whether or not animated accessories are used are independent of these definitions and really a decision the modeler makes to enjoy his or her involvement in the hobby.
The prototype for these standards are North American rail, where the standard gauge (railhead spacing) is 4 feet, 8-1/2" wide. Narrow gauges covered here are Sn3 (3-foot spacing), and Sn2 (2-foot spacing). Sn42, which is also modeled (42" between the rails, and using HO-scale track), appears to not have any formal standards.
The NMRA standards that start with "S-" are model railroading industry standards as maintained by the NMRA and NASG. The ones starting with "RP-" are "recommended-practices", which are not standards, but are commonly followed nonetheless.
Click the link of interest below, or just scroll down the page.
This table shows the minimum and maximum measurements of the distance between the railheads of general straight track for S-scale (denoted as "G" in diagrams). For hi-rail/deep-flange, minimum rail size is code 125 (see NMRA S-1.3). Note that for some, the gauge-maximum is different at the turnout frog than it is elsewhere (minimum is always the same).
| Gauge (G) | Gauge at Turnout Frog (G) | min | max | max |
|---|---|---|---|
| standard-gauge | 0.883" | 0.905" | 0.895" |
| 22.43 mm | 22.99 mm | 22.73 mm | |
| hi-rail | 0.883" | 0.905" | 0.895" |
| 22.43 mm | 22.99 mm | 22.73 mm | |
| proto:64 | 0.883" | 0.902" | 0.902" |
| 22.43 mm | 22.91 mm | 22.91 mm | |
| narrow-gauge (Sn3) | 0.563" | 0.585" | 0.575" |
| 14.30 mm | 14.86 mm | 14.60 mm | |
| narrow-gauge (Sn3, proto:64) | 0.563" | 0.582" | 0.582" |
| 14.30 mm | 14.78 mm | 14.78 mm | |
| narrow-gauge (Sn2) | 0.413" | 0.423" | 0.423" |
| 10.49 mm | 10.74 mm | 10.74 mm |
This RP deals with the minimum track curvature recommended for the given equipment to be run on the track.
| Equipment | Minimum Turnout # | Minimum Curve | Prototype Radius | Model Radius |
|---|---|---|---|---|
| Street cars: | 2.5 | 36' | 7" | |
| Interurbans (in-city-streets): | 3 | 180° | 50' | 9.5" |
| Interurbans & trailers up to 40': | 3 | 100° | 65' | 12" |
| Interurbans & trailers up to 50': | 4 | 80° | 78' | 14.5" |
| Interurbans & trailers up to 64': | 4 | 60° | 100' | 19" |
| Electric up to 50' passenger to 60' (no diaphragms) freight to 50': |
5 | 50° | 118' | 22.5" |
| Electric up to 60' passenger to 60' (diaphragms): |
5 | 40° | 146' | 27.5" |
| Electric up to 70' passenger to 70': |
6 | 35° | 166' | 31" |
| Small steam/diesel with 4 wheels cars to 40': |
4 | 60° | 100' | 19" |
| Steam up to 11' rigid wheel-base diesel up to 40' (4-wheeled) cars up to 50': |
5 | 50° | 118' | 22.5" |
| Steam up to 14' rigid wheel-base diesel up to 50' (4-wheeled) cars up to 60': |
5 | 40° | 146' | 27.5" |
| Steam up to 17' rigid wheel-base diesel up to 60' (4-wheeled) passenger up to 60' freight up to 50': |
6 | 35° | 166' | 31" |
| Steam up to 20' rigid wheel-base diesel up to 60' (4-/6-wheeled) passenger up to 70' freight up to 62': |
6 | 30° | 193' | 36" |
| Steam up to 24' rigid wheel-base diesel up to 70' (4-/6-wheeled) passenger up to 80 freight up to 85': |
6 | 25° | 231' | 43.5" |
| Steam up to 28' rigid wheel-base: | 7 | 20° | 288' | 54" |
This RP deals with the actual shape and dimensions of the rail. It lists the actual dimensions for the individual parts of a piece of rail of codes 32 through 297. Those are probably only useful to model rail manufacturers. However, it also provides a table that matches recommended scale rail codes to the prototype type of rail modeled, which, for S-scale, has been reproduced below. Note that in model railroading, "code" represents the height of the rail in terms of 0.001 (one-thousandths-of-an-inch). So, "code 125" is actually 0.125 inches (1/8") tall.
| Prototype Standard | Prototype Weight (lbs/yard) | Prototype Rail Height (inches) | Model Rail (code) |
|---|---|---|---|
| PRR: | 155 | 8.000 | 125 |
| AREA: | 140 | 7.312 | 114 |
| AREA: | 132 | 7.125 | 111 |
| AREA: | 115 | 6.625 | 104 |
| AREA: | 100 | 6.000 | 94 |
| AREA: | 90 | 5.625 | 88 |
| ASCE: | 85 | 5.188 | 81 |
| ASCE: | 80 | 5.000 | 78 |
| ASCE: | 75 | 4.812 | 75 |
| ASCE: | 70 | 4.625 | 72 |
| ASCE: | 65 | 4.438 | 69 |
| ASCE: | 60 | 4.250 | 66 |
| ASCE: | 55 | 4.062 | 63 |
| ASCE: | 50 | 3.875 | 61 |
| ASCE: | 45 | 3.688 | 58 |
| ASCE: | 40 | 3.500 | 55 |
| ASCE: | 35 | 3.312 | 52 |
| ASCE: | 30 | 3.125 | 49 |
| ASCE: | 25 | 2.750 | 43 |
In North America, standard-gauge track uses wooden railroad ties which measure 8'6" in length, 7" tall, and 9" wide. The distance between the ties is typically 21", so with 9"-wide ties that makes the gap between ties 12". This equates to 3,000 ties per mile. Wooden ties provide "give" which makes the rail and the equipment riding on the rail last longer. Wooden ties are impregnated with a creosote preservative so that they can last 25 to 30 years. They weigh around 225lbs each. Concrete ties are being used in newer track in North America. Their "give" is between the ties and the ballast. They weigh around 700lbs each.
NMRA S-1.1 Standards for Proto Models covers standard- and narrow-gauge proto:64 measurements (PDF).
NMRA S-1.2 Standards for Scale Models covers standard- and narrow-gauge general measurements (PDF).
NMRA S-1.3 Standards for Deep Flange Models covers hi-rail/deep-flange general measurements (PDF).
NMRA RP-10 Trackwork General (PDF).
NMRA RP-11 Curvature and Rolling Stock (PDF).
NMRA RP-15.1 Rail (PDF).
Prototype Rail Specifications (includes railroad-specific ones).
"The Railroad What It Is, What it Does" by John H. Armstrong.
Demystifying The NMRA Standards (four-part video series by FastTracks).
This table shows the coupler height for S-scale, as measured from the top of rail to the center of the knuckle. The prototype has a tolerance of +/-1.5 inches (3.81cm).
| Coupler Height | Tolerance (+/-) | |
|---|---|---|
| standard-gauge | 0.531" | 0.023" |
| 13.48 mm | 0.58 mm | |
| narrow-gauge | 0.4063" | 0.023" |
| 10.32 mm | 0.58 mm |
NMRA S-2 Coupler Standards covers standard- and narrow-gauge measurements (PDF).
The dark-colored rails represent the stock rails. The letters in the diagram represent measurements that are provided in the tables, and only applies to non-proto:64 standards. For "G", which is the general track spacing, see S-1 above (specifically its third data column).
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Check Gauge (C) | 0.839 | 0.848 | 21.31 | 21.54 |
| Span (S) | 0.789 | 0.793 | 20.04 | 20.14 |
| Flangeway at Wing Rail (F) | 0.035 | 0.050 | 0.89 | 1.27 |
| Flange Depth (H) | 0.025 | 0.64 | ||
| Switch Point Spread (P) | 0.818 | 0.824 | 20.78 | 20.93 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Check Gauge (C) | 0.839 | 0.848 | 21.31 | 21.54 |
| Span (S) | 0.791 | 0.797 | 20.09 | 20.24 |
| Flangeway at Wing Rail (F) | 0.035 | 0.050 | 0.89 | 1.27 |
| Flange Depth (H) | 0.094 | 2.39 | ||
| Switch Point Spread (P) | 0.816 | 0.822 | 20.73 | 20.88 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Check Gauge (C) | 0.519 | 0.528 | 13.18 | 13.41 |
| Span (S) | 0.469 | 0.473 | 11.91 | 12.01 |
| Flangeway at Wing Rail (F) | 0.035 | 0.050 | 0.89 | 1.27 |
| Flange Depth (H) | 0.025 | 0.64 | ||
| Switch Point Spread (P) | 0.498 | 0.504 | 12.65 | 12.80 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Check Gauge (C) | 0.377 | 0.383 | 9.58 | 9.73 |
| Span (S) | 0.337 | 0.341 | 8.56 | 8.66 |
| Flangeway at Wing Rail (F) | 0.030 | 0.040 | 0.77 | 1.02 |
| Flange Depth (H) | 0.023 | 0.58 | ||
| Switch Point Spread (P) | 0.359 | 0.365 | 9.12 | 9.27 |
The diagram below applies only to proto:64 standards for standard- and narrow-gauge tables below. For "G", which is the general track spacing, see S-1 above (specifically its third data column).
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Check Gauge (C) | 0.851 | 0.853 | 21.62 | 21.67 |
| Span (S) | 0.814 | 0.823 | 20.68 | 20.90 |
| Flangeway at Frog (F) | 0.028 | 0.030 | 0.710 | 0.760 |
| Flangeway at Guard (F) | 0.031 | 0.031 | 0.790 | 0.790 |
| Flange Depth (H) | 0.020 | 0.510 | ||
| Switch Point Spread (P) | 0.809 | 20.55 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Check Gauge (C) | 0.530 | 0.533 | 13.46 | 13.54 |
| Span (S) | 0.494 | 0.503 | 12.55 | 12.78 |
| Flangeway at Frog (F) | 0.028 | 0.030 | 0.710 | 0.760 |
| Flangeway at Guard (F) | 0.032 | 0.032 | 0.810 | 0.810 |
| Flange Depth (H) | 0.020 | 0.510 | ||
| Switch Point Spread (P) | 0.488 | 12.40 |
This RP deals with the actual dimensions of the various pieces and rails that make up a turnout. The NMRA has documents showing the individual measurements labeled in the diagrams below for both straight and curved turnouts, in frog numbers from 4 through 20. Click the diagram to see a larger version. The documents for S-scale are copied here to our web site, because the NMRA keeps them in one large .zip file for all of the scales together. So, rather than having to download that entire file, and then needing to extract the one or two documents that you actually want, you can download them directly from our web site (see links below).
standard straight turnout (PDF)
standard curved turnout (PDF)
hi-rail straight turnout (PDF)
hi-rail curved turnout (PDF)
proto:64 straight turnout (PDF)
proto:64 curved turnout (PDF)
NMRA S-3.1 Standards for Proto Models covers standard- and narrow-gauge proto:64 measurements (PDF).
NMRA S-3.2 Standards for Scale Models covers standard- and narrow-gauge general measurements (PDF).
NMRA S-3.3 Standards for Deep Flange Models covers hi-rail/deep-flange general measurements (PDF).
NMRA RP-12 Turnouts - General: general, non-scale-specific information (PDF).
NMRA RP-13.5 Guard Rail & Frog Relationship: provides more details about diagram item #30 (PDF).
NMRA RP-13.6 Guard Rails: duplicates guard rail dimensions #32, #33, #34 (PDF).
NMRA RP-13.7 Frog & Wing Rails: duplicates frog and wing rail dimensions #19, #20, #21, #22 (PDF).
NMRA RP-13.8 Flangeway Flares: provides more details about how to form flangeway flares (PDF).
Fast Tracks Templates: standard-gauge: turnouts, wyes, 3-ways, crossings, and slip switches.
Fast Tracks Templates: narrow-gauge (Sn3): turnouts, wyes, 3-ways, crossings, and dual-gauge.
Fast Tracks Templates: narrow-gauge (Sn2): turnouts and wyes.
The letters in the diagram represent measurements that are provided in the tables.
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Wheel Check Gauge (K) | 0.830 | 0.839 | 21.08 | 21.31 |
| Back to Back (B) | 0.800 | 0.809 | 20.32 | 20.55 |
| Wheel Width (N) | 0.110 | 0.110 | 2.79 | 2.79 |
| Flange Width (T) | 0.030 | 0.76 | ||
| Flange Depth (D) | 0.030 | 0.76 | ||
| Wheel Code (W) | 110 | 110 | 110 | 110 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Wheel Check Gauge (K) | 0.770 | 0.777 | 19.56 | 19.74 |
| Back to Back (B) | 0.705 | 0.712 | 17.91 | 18.09 |
| Wheel Width (N) | 0.172 | 4.37 | ||
| Flange Width (T) | 0.063 | 0.067 | 1.60 | 1.70 |
| Flange Depth (D) | 0.095 | 2.41 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Wheel Check Gauge (K) | 0.510 | 0.519 | 12.95 | 13.18 |
| Back to Back (B) | 0.480 | 0.489 | 12.19 | 12.42 |
| Wheel Width (N) | 0.110 | 0.110 | 2.79 | 2.79 |
| Flange Width (T) | 0.030 | 0.76 | ||
| Flange Depth (D) | 0.030 | 0.76 | ||
| Wheel Code (W) | 110 | 110 | 110 | 110 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Wheel Check Gauge (K) | 0.370 | 0.377 | 9.40 | 9.58 |
| Back to Back (B) | 0.345 | 0.352 | 8.76 | 8.94 |
| Wheel Width (N) | 0.088 | 0.088 | 2.24 | 2.24 |
| Flange Width (T) | 0.025 | 0.64 | ||
| Flange Depth (D) | 0.023 | 0.58 | ||
| Wheel Code (W) | 88 | 88 | 88 | 88 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Wheel Check Gauge (K) | 0.842 | 0.850 | 21.39 | 21.59 |
| Back to Back (B) | 0.825 | 0.834 | 20.96 | 21.18 |
| Wheel Width (N) | 0.087 | 0.092 | 2.21 | 2.34 |
| Flange Width (T) | 0.017 | 0.019 | 0.43 | 0.48 |
| Flange Depth (D) | 0.018 | 0.020 | 0.46 | 0.51 |
| Wheel Gauge (K + T) | 0.859 | 0.872 | 21.82 | 22.15 |
| min (inches) | max (inches) | min (mm) | max (mm) | |
|---|---|---|---|---|
| Wheel Check Gauge (K) | 0.522 | 0.529 | 13.26 | 13.44 |
| Back to Back (B) | 0.505 | 0.514 | 12.83 | 13.06 |
| Wheel Width (N) | 0.087 | 0.092 | 2.21 | 2.34 |
| Flange Width (T) | 0.017 | 0.019 | 0.43 | 0.48 |
| Flange Depth (D) | 0.018 | 0.020 | 0.46 | 0.51 |
| Wheel Gauge (K + T) | 0.539 | 0.552 | 13.69 | 14.02 |
This RP deals with the dimensions of trucks. The purpose is to make easy interchanges of trucks between cars possible. The diagram on the right applies to the S-scale measurements listed below.
(P) Kingpin Size: 0.112" (#4)
(E) Truck Bolster Hole: 0.116 (#32 Drill)
(D) Center Plate Diameter: 3/8" max.
(Bc) Center Bolster Bearing (freight): 13/32"
(Bc) Center Bolster Bearing (passenger): 1/2"
(Bs) Side Bolster Bearing: not recommended
(Si) Distance Side (inside): not recommended
(So) Distance Side (outside): not recommended
This RP deals with the dimensions of journals. The diagram on the right applies to the S-scale measurements listed below.
(J) Journal Bore min. diameter: 0.067"
(V) Journal Bore min. depth: 0.123"
(X) Journal Bore min. span: 1.314"
(W) Journal Face min. spacing: 1.068"
This RP deals with the dimensions of axles. The diagram on the right applies to the S-scale measurements listed below. The standard lists this specific note for S-scale: "Axle insulating bushings are optional, and, if used, may extend beyond the outer face of the wheel. The maximum allowable distance over the outer faces of bushings shall be 1.064 inches."
(A) Axle Diameter max.: 0.063"
(Y+) Shoulder min.: 3/32"
(U) Axle Length max.: 1.310"
NMRA S-4.1 Standards for Proto Models covers standard- and narrow-gauge proto:64 measurements (PDF).
NMRA S-4.2 Standards for Scale Models covers standard- and narrow-gauge general measurements (PDF).
NMRA S-4.3 Standards for Deep Flange Models covers hi-rail/deep-flange general measurements (PDF).
S-Helper Service's Hi-rail Wheel Contour (.gif), provided by Don Thompson.
S-Helper Service's Hi-rail Wheelset (.gif), provided by Don Thompson.
NMRA RP-21.2 Solid Couplers (PDF); probably only of interest to coupler manufacturers.
NMRA RP-23 Bolsters (PDF).
NMRA RP-24.1 Journals (PDF).
NMRA RP-24.3 Axles (PDF).
NMRA RP-25 Wheel Contour (PDF).
This section concerns itself with standards for traction (i.e. overhead-wire) motive power.
| Imperial | Metric | |
|---|---|---|
| Overhead Contact Wire Gauge (AWG) | 26 | 26 |
| Overhead Contact Wire Diameter | 0.016" | 0.41 mm |
| Nominal Wire Height (City/Interurban) | 3-15/16" | 100 mm |
| Nominal Wire Height (Heavy Railroad) | 4-5/16" | 110 mm |
| Pantograph Operation Maximum Offset | 5/16" | 7.9 mm |
| Pantograph Contact Shoe Min. Length | 3/4" | 19.0 mm |
| Pole Base Mounting | #60 pin (3.8") | |
| Pole Base Mounting Car Receptacle | threaded 2-56 |
The diagram above applies to the table below.
| Imperial | Metric | |
|---|---|---|
| Trolley Wheel Width (W) | 1/16" (+/-5%) | 1.6 mm (+/-5%) |
| Trolley Wheel Diameter (D) | 1/8" (+/-5%) | 3.2 mm (+/-5%) |
| Contact Force (minimum) | 0.3 oz | 0.08 N |
| Contact Force (maximum) | 0.4 oz | 0.11 N |
The diagram above applies to the table below.
| Imperial | Metric | |
|---|---|---|
| Third Rail Height Above Railhead (E) | 3/32" | 2.4 mm |
| Third Rail Offset from Gauge Line (R) | 7/16" | 11.1 mm |
NMRA S-5 Traction Power Collection (PDF).
These clearances and track centers provide for interchange and satisfactory operation of interurban and street railway equipment only. The outside clearance is the amount of space to leave unobstructed from the outside-of-the-curve rail out. The inside clearance is the amount of space to leave unobstructed from the inside-of-the-curve rail out. Track center is measured between two tracks' centerlines (midway between the rails).
| Prototype Radius | Model Radius | Clearance (inside) | Clearance (outside) | Track Center |
|---|---|---|---|---|
| 35' | 6-9/16" | 2-9/32" | 1-25/32" | 3-3/4" |
| 45' | 8-7/16" | 2-1/32" | 1-11/16" | 3-1/2" |
| 60' | 11-1/4" | 1-25/32" | 1-5/8" | 3-1/4" |
| 75' | 14-1/16" | 1-21/32" | 1-17/32" | 3-1/16" |
| 100' | 18-3/4" | 1-17/32" | 1-7/16" | 2-29/32" |
| 125' | 23-7/16" | 1-7/16" | 1-13/32" | 2-13/16" |
| 150' | 28-1/8" | 1-13/32" | 1-3/8" | 2-3/4" |
| 175' | 32-13/16" | 1-3/8" | 1-5/16" | 2-23/32" |
| 200' | 37-1/2" | 1-5/16" | 1-9/32" | 2-11/16" |
| straight | 1-1/8" | 1-1/8" | 2-3/8" |
NMRA S-6 Interurban Clearance & Track Centers (PDF).
This standard specifies the clearances for bridges, structures, and tangent tracks for Old Time (pre-1920), Classic (1920-1969), and Modern (post-1983) eras.
| Old Time | Classic | Modern | inches | mm | inches | mm | inches | mm |
|---|---|---|---|---|---|---|
| (A) | 1-1/8 | 29 | 1-13/32 | 36 | 1-11/16 | 43 |
| (B) | 9/16 | 14 | 3/4 | 19 | 1-1/8 | 29 |
| (C) | 3/4 | 19 | 1-1/8 | 29 | 9/16 | 14 |
| (D) | 1-7/8 | 48 | 2-1/4 | 57 | 3 | 76 |
| (E) | 9/16 | 14 | 3/4 | 19 | 3/4 | 19 |
| (F) | 3/8 | 10 | 15/32 | 12 | (n/a) | (n/a) |
| (G) | 1-1/32 | 26 | 1-1/8 | 29 | 1-1/8 | 29 |
| (H) | 3-3/16 | 81 | 4-1/8 | 105 | 4-5/16 | 110 |
| (P) | 1-1/32 | 26 | 1-1/8 | 29 | 1-1/16 | 27 |
The NMRA S-7 Clearances (PDF).
This standard specifies the distance between two tracks' centerlines (midway between the rails). Curved track is assumed to be eased.
| Class II | Class I | Class Ia | diesel: small 4-wheeled steam: small, geared (logging, branch, old-time) |
diesel: large 4-, 6-wheeled steam: longer (x-x-2) |
steam: larger (x-x-4), cars: articulated passenger | usage | actual | scale | actual | scale | actual | scale |
|---|---|---|---|---|---|---|
| Handling (e.g. in yards): | 2-13/16" | 15' | 2-13/16" | 15' | 2-13/16" | 15' |
| Straight: | 2-7/16" | 13' | 2-7/16" | 13' | 2-7/16" | 13' |
| 215"-radius: | 2-7/16" | 13' | 2-9/16" | 13'8" | 2-11/16" | 14'4" |
| 108"-radius: | 2-1/2" | 13'4" | 2-5/8" | 14' | 2-7/8" | 15'4" |
| 72"-radius: | 2-9/16" | 13'8" | 2-3/4" | 14'8" | 3-1/16" | 16'4" |
| 54"-radius: | 2-5/8" | 14' | 2-13/16" | 15' | 3-1/4" | 17'4" |
| 43"-radius: | 2-11/16" | 14'4" | 2-7/8" | 15'4" | 3-3/8" | 18' |
| 36"-radius: | 2-3/4" | 14'8" | 3" | 16' | * | * |
| 31"-radius: | 2-13/16" | 15' | 3-1/8" | 16'8" | * | * |
| 27"-radius: | 2-7/8" | 15'4" | * | * | * | * |
| 25"-radius: | 3" | 16' | * | * | * | * |
* Not prohibited, but also not recommended.
| usage | actual | scale |
|---|---|---|
| Handling (e.g. in yards): | 2-1/4" | 12' |
| Straight: | 2-1/16" | 11' |
| 215"-radius: | 2-1/16" | 11' |
| 108"-radius: | 2-1/16" | 11' |
| 72"-radius: | 2-1/8" | 11'4" |
| 54"-radius: | 2-1/4" | 12' |
| 43"-radius: | 2-3/8" | 12'8" |
| 36"-radius: | 2-7/16" | 13' |
| 31"-radius: | 2-9/16" | 13'8" |
| 27"-radius: | 2-5/8" | 14' |
| 25"-radius: | 2-3/4" | 14'8" |
The NMRA S-8 Track Centers (PDF).
The design specifications for a three-point track gauge.
| Class II | Class I | Class Ia | diesel: small 4-wheeled steam: small, geared (logging, branch, old-time) |
diesel: large 4-, 6-wheeled steam: longer (x-x-2) |
steam: larger (x-x-4), articulated passenger cars |
usage | Gage Length (L) | Gage Length (L) | Gage Length (L) |
|---|---|---|---|
| 43"-radius: | 2-7/16" | ||
| 31"-radius: | 2-3/32" | ||
| 25"-radius: | 1-7/8" |
The NMRA RP-8 Three Point Track Gage (PDF).
S-scale car weight standard is: 2 ounces plus 1/2-ounce per inch of car body length. A couple of examples are:
- a standard 40-foot box car should weigh 5.75 ounces (2oz + (7.5" x 0.5oz)), or 163 grams for a 19.1cm car.
- a standard 50-foot reefer should weigh 6.7 ounces (2oz + (9.375" x 0.5oz)), or 190 grams for a 23.8cm car.
S-scale car weight standard is: 1 ounce plus 1/2-ounce per inch of car body length.
The NMRA RP-20.1 Car Weight (PDF).
The NASG S-MOD Standards were developed so that S-scale modelers could gather from anywhere and easily join their modules into functioning, hassle-free layouts. These standards have been accepted by the NMRA Engineering Committee as the basis for the NMRA's S-scale module standards. They accommodate standard-gauge, narrow-gauge, and/or hi-rail. Track and wheel dimensional standards match those described above.
NASG S-MOD Standards (PDF)
NASG S-MOD Layout Electrical System (PDF)
NMRA MS-1.0 Standard-gauge module standard (PDF).
NMRA MS-1.0 Narrow-gauge module standard (PDF).
NMRA MS-1.2 Traction module standard (PDF).
NMRA MRP-1.0 Standard-gauge module recommended practices (PDF).
NMRA MRP-1.1 Narrow-gauge module recommended practices (PDF).
NMRA MRP-1.2 Traction module recommended practices (PDF).
NMRA MRP-1.2a Traction module recommended practices (PDF).
Don Thompson and Don DeWitt wrote a four-part article for the S Gauge Herald on how to construct S-MOD modules. These have been scanned into PDF form here:
There are currently no known standards for the S-scale standard-gauge or Sn3 versions of Free-mo. However, there is one for Sn2 modules. In general, the few groups that have these types of modules simply set their own internal standards (the Canadian S Scale Workshop is one prime example of this type of layout).
T-TRAK was originally developed for N-scale, but the standard now includes Z- through O-scale. The standard has very few requirements, making creativity a high priority. It is a simple, and easy-to-transport wooden box upon which track is attached. Originally developed in Japan where space is at a premium and modelers attending local trains shows have to use public transportation, the small boxes make them ultra-portable, perfect for the modeler with limited space. Set-up at shows is typically done using standard folding-legs tables, upon which the modules are placed.
In the Sep/Oct 2016 issue of the NASG's The Dispatch a photo is shown of an S-scale T-TRAK modular layout that was set up at the 2016 NASG Convention. Charles Malinowski, member of the Hoosier S Gaugers club, and others developed this layout. It currently consists of 4 straight modules and 4 curved modules. The layout has been taken to several area train shows in Indiana. Charles has written an article for the The Dispatch in 2017 about how they built their layout. If you are interested in T-TRAK for S-scale, contact the NASG webmaster for Charles' contact info, or log into the Members Only section of this web site to get Charles' info. He will be happy to answer any questions you might have about S-scale T-TRAK.
The T-TRAK standard for S-scale (scroll to the bottom of that page).
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