STANDARD© NATIONAL MODEL RAILROAD ASSOCIATION

StandardTitle
VersionPage

S-3.2
Scale Track, Standard ScaleFebruary 2010
1 of 3The Span, S, is derived by knowing S = C-F.
C is the primary controlling dimension.

Standard S3.2 Guarded using Target and Asymmetric Imperial (inch) Tolerance
GCSFPScale
Check Gage
Gage at Frog
Span
Flangeway
PointsTarget Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus
1"
1:12 4.752 0.060 0.002 4.586 0.011 0.004 4.366 0.004 0.002 0.218 0.002 0.065 4.561 0.004 0.004
3/4"
1:16 3.502 0.038 0.002 3.353 0.014 0.004 3.172 0.004 0.002 0.179 0.002 0.046 3.325 0.004 0.004
F
1:20.3 2.783 0.014 0.002 2.683 0.013 0.004 2.583 0.013 0.004 0.096 0.004 0.006 2.656 0.004 0.004
Fn3 1:20.3 1.772 0.010 0.006 1.652 0.010 0.004 1.550 0.005 0.015 0.115 0.002 0.023 1.628 0.004 0.004
Large Scale Standards on Separate Page
LS VariedO
1:48 1.252 0.012 0.002 1.181 0.013 0.002 1.102 0.002 0.002 0.077 0.002 0.021 1.156 0.002 0.004
On3
1:48 0.752 0.012 0.002 0.707 0.010 0.002 0.654 0.002 0.002 0.051 0.002 0.018 0.685 0.002 0.004
On30 1:48 0.651 0.010 0.002 0.607 0.007 0.002 0.557 0.002 0.002 0.048 0.002 0.013 0.588 0.002 0.004
On2
1:48 0.502 0.009 0.002 0.457 0.007 0.002 0.407 0.002 0.002 0.048 0.002 0.012 0.438 0.002 0.004
S1:64 0.885 0.010 0.002 0.841 0.007 0.002 0.791 0.002 0.002 0.048 0.002 0.013 0.822 0.002 0.004
Sn31:64 0.565 0.010 0.002 0.521 0.007 0.002 0.471 0.002 0.002 0.048 0.002 0.013 0.502 0.002 0.004
Sn2
1:64 0.415 0.008 0.002 0.379 0.004 0.002 0.339 0.002 0.002 0.038 0.002 0.008 0.363 0.002 0.004
OO 1:76.2 0.752 0.009 0.002 0.707 0.007 0.002 0.657 0.002 0.002 0.048 0.002 0.012 0.688 0.002 0.004
HO 1:87.1 0.651 0.010 0.002 0.607 0.007 0.002 0.557 0.002 0.002 0.048 0.002 0.013 0.588 0.002 0.004
HOn3 1:87.1 0.415 0.008 0.002 0.379 0.004 0.002 0.339 0.002 0.002 0.038 0.002 0.008 0.363 0.002 0.004
HOn2 1:87.1 0.278 0.007 0.002 0.248 0.004 0.002 0.215 0.002 0.002 0.031 0.002 0.007 0.234 0.002 0.002
TT1:120 0.473 0.006 0.002 0.439 0.003 0.002 0.403 0.002 0.002 0.034 0.002 0.005 0.426 0.002 0.002
TTn42 1:120 0.355 0.004 0.002 0.325 0.001 0.002 0.295 0.001 0.002 0.028 0.002 0.001 0.314 0.002 0.002
TTn3 1:120 0.302 0.004 0.002 0.272 0.002 0.002 0.242 0.002 0.002 0.028 0.002 0.002 0.260 0.002 0.002
N1:160 0.355 0.004 0.002 0.325 0.001 0.002 0.295 0.001 0.002 0.028 0.002 0.001 0.314 0.002 0.002
Nn3 1:160 0.258 0.003 0.002 0.232 0.003 0.002 0.207 0.002 0.002 0.023 0.002 0.002 0.219 0.002 0.002
Nn2 1:160 0.179 0.002 0.002 0.152 0.006 0.002 0.127 0.002 0.002 0.023 0.002 0.004 0.136 0.002 0.002
Z
1:220 0.259 0.008 0.002 0.238 0.004 0.002 0.213 0.002 0.002 0.023 0.002 0.008 0.224 0.002 0.002
Scale
Ratio

HWheelMIN CODE
0.140 1/2"
0.094 13/32"
0.084 284
0.066 250
0.045
0.026
0.025
0.025
0.025
0.025
0.023
0.025
0.025
0.023
0.020
0.023
0.020
0.020
0.020
0.016
0.016
0.016

145
116
110
110
110
110
88
110
110
8872
79
72
72
7254
54
54

Track NOTES:
1. When wheels are used with deeper flanges - see STANDARD S3.3.
2. The F limit applies only to the wing rail, and the C limit applies only to the guard rail. Both apply to thesame rail only in special work such as a crossing.
3. For a full discussion of minimum radius, minimum turnout and radius equivalents of degrees of curvature.
etc., see S-8 and RP-11.
4. Guard and wing rails shall be flared to a minimum dimension across the flared flangeway end of 1.5 xFmax. Flare angle shall not exceed 10 degrees, and the Flare must disappear before reaching the working
area of its rail.
5. These track dimensions are more restrictive with Gmax for guarded trackwork, for general track see STANDARD S3.1.
6. Metric measurements are found on page 2.
7. Please see S4.2 and RP-25 Wheel Contour for the appropriate wheel profile.
8. O-scale frog flangeway (F) is recommended with a target for code 145 wheels at 0.071”.
Copyright 1986-2010, by National Model Railroad Association, Inc.

Page 1 of 3

STANDARD© NATIONAL MODEL RAILROAD ASSOCIATION

StandardTitleVersionPageS-3.2
Scale Track, Standard Scale
February 2010
2 of 3The Span, S, is derived by knowing S = C-F.
C is the primary controlling dimension.
Standard S3.2 Guarded using Target and Asymmetric METRIC (mm) Tolerance
GCSFP
Scale
PointsGage at Frog
Check Gage
Span
Flangeway
Target Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus
1"
1:12 120.70 1.52 0.05 116.48 0.28 0.10 110.90 0.10 0.05 5.54 0.05 1.65 115.85 0.10 0.10
3/4"
1:16 88.95 0.97 0.05 85.17 0.36 0.10 80.57 0.10 0.05 4.55 0.05 1.17 84.46 0.10 0.10
F
1:20.3 70.69 0.36 0.05 68.15 0.33 0.10 65.61 0.33 0.10 2.44 0.10 0.15 67.46 0.10 0.10
Fn3 1:20.3 45.00 0.25 0.15 42.00 0.25 0.10 39.37 0.13 0.38 2.92 0.05 0.58 41.35 0.10 0.10
LS
Large Scale Standards on Separate Page
VariedO
1:48 31.80 0.30 0.05 30.00 0.33 0.05 27.99 0.05 0.05 1.96 0.05 0.53 29.36 0.05 0.10
On3
1:48 19.10 0.30 0.05 17.96 0.25 0.05 16.61 0.05 0.05 1.30 0.05 0.46 17.40 0.05 0.10
On30 1:48 16.54 0.25 0.05 15.42 0.18 0.05 14.15 0.05 0.05 1.22 0.05 0.33 14.94 0.05 0.10
On2
1:48 12.75 0.23 0.05 11.61 0.18 0.05 10.34 0.05 0.05 1.22 0.05 0.30 11.13 0.05 0.10
S
1:64 22.48 0.25 0.05 21.36 0.18 0.05 20.09 0.05 0.05 1.22 0.05 0.33 20.88 0.05 0.10
Sn3
1:64 14.35 0.25 0.05 13.23 0.18 0.05 11.96 0.05 0.05 1.22 0.05 0.33 12.75 0.05 0.10
Sn2
1:64 10.54 0.20 0.05 9.63 0.10 0.05 8.61 0.05 0.05 0.97 0.05 0.20 9.22 0.05 0.10
OO 1:76.2 19.10 0.23 0.05 17.96 0.18 0.05 16.69 0.05 0.05 1.22 0.05 0.30 17.48 0.05 0.10
HO1:87.1 16.54 0.25 0.05 15.42 0.18 0.05 14.15 0.05 0.05 1.22 0.05 0.33 14.94 0.05 0.10
HOn3 1:87.1 10.54 0.20 0.05 9.63 0.10 0.05 8.61 0.05 0.05 0.97 0.05 0.20 9.22 0.05 0.10
HOn2 1:87.1 7.06 0.18 0.05 6.30 0.10 0.05 5.46 0.05 0.05 0.79 0.05 0.18 5.94 0.05 0.05
TT1:120 12.01 0.15 0.05 11.15 0.08 0.05 10.24 0.05 0.05 0.86 0.05 0.13 10.82 0.05 0.05
TTn42 1:120 9.02 0.10 0.05 8.26 0.03 0.05 7.49 0.03 0.05 0.71 0.05 0.03 7.98 0.05 0.05
TTn3 1:120 7.67 0.10 0.05 6.91 0.05 0.05 6.15 0.05 0.05 0.71 0.05 0.05 6.60 0.05 0.05
N1:160 9.02 0.10 0.05 8.26 0.03 0.05 7.49 0.03 0.05 0.71 0.05 0.03 7.98 0.05 0.05
Nn3 1:160 6.55 0.08 0.05 5.89 0.08 0.05 5.26 0.05 0.05 0.58 0.05 0.05 5.56 0.05 0.05
Nn2 1:160 4.55 0.05 0.05 3.86 0.15 0.05 3.23 0.05 0.05 0.58 0.05 0.10 3.45 0.05 0.05
Z
1:220 6.58 0.20 0.05 6.05 0.10 0.05 5.41 0.05 0.05 0.58 0.05 0.20 5.69 0.05 0.05
Scale
Ratio

HWheel

MIN
3.56
2.39
2.13
1.68

CODE
1/2"
13/32"
284
250

1.14
0.66
0.64
0.64
0.64
0.64
0.58
0.64
0.64
0.58
0.51
0.58
0.51
0.51
0.51
0.41
0.41
0.41

145
116
110
110
110
110
88
110
110
88
7279
72
72
72
54
54
54

Track NOTES:
1. When wheels are used with deeper flanges - see STANDARD S3.3.
2. The F limit applies only to the wing rail, and the C limit applies only to the guard rail. Both apply to thesame rail only in special work such as a crossing.
3. For a full discussion of minimum radius, minimum turnout and radius equivalents of degrees of curvature.
etc., see S-8 and RP-11.
4. Guard and wing rails shall be flared to a minimum dimension across the flared flangeway end of 1.5 xFmax. Flare angle shall not exceed 10 degrees, and the Flare must disappear before reaching the workingarea of its rail.
5. These track dimensions are more restrictive with Gmax for guarded trackwork, for general track - see
STANDARD S3.1.
6. O-scale frog flangeway (F) is recommended with a target for code 145 wheels at 1,8mm.
7. Imperial measurements are found on page 1.

Copyright 1986-2010, by National Model Railroad Association, Inc.

Page 2 of 3

STANDARD© NATIONAL MODEL RAILROAD ASSOCIATION

StandardTitle
VersionPage

S-3.2
Scale Track, Standard Scale
February 2010
3 of 3The Span, S, is derived by knowing S = C-F.
C is the primary controlling dimension.
Standard S3.2 Guarded using Target and Asymmetric Imperial (inch) Tolerance
GCSFPScale
Gage at Frog
PointsCheck Gage
Span
Flangeway
Target Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus
LS Varied 1.772 0.010 0.006 1.652 0.010 0.004 1.550 0.005 0.015 0.115 0.002 0.023 1.629 0.003 0.005
Scale
Ratio

Scale
LS

Standard S3.2 Guarded using Target and Asymmetric METRIC (mm) Tolerance
GPCSF
Gage at Frog
Check Gage
Span
Flangeway
PointsTarget Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus Target Plus Minus
0.25
0.15
41.96
0.25
0.10
39.37
0.13
0.38
2.92
0.05
0.58
41.38
0.08
0.13
Varied 45.01
ScaleRatio

HMIN
0.118

HMIN
3.00

Track NOTES:1) The term “LS” for ”Large Scales” standards covers all common commercial scales running on LS 45mmgauge track (1:32, 1:29, 1:24, 1:22.5, and 1:20.3) without regard as to whether the trains are standard or
narrow gauge.
2) Due to the inherent nature of large scale trains, the wheel and track standards for “Standard” (Sx.2) and“Deep Flange” (Sx.3) are identical except in terms of flange width and depth, thus the track H depth also ischanged.
3) With regard to 1:20.3 (also designated "F" scale), trains built to that scale running on LS 45mm gauge track
are also classified Fn3. Standards for Fn3 track and wheels are identical to those for LS, with exception
given to more specific targets given for tread width and flange depth. Track standards for Fn3 are to beidentical to those used for LS 45mm gauge.

Copyright 1986-2010, by National Model Railroad Association, Inc.

Page 3 of 3