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S-3.1 Trackwork, Proto & Fine Scales

S-3.1 Trackwork, Proto & Fine Scales

S-3.1

 

Note: The Proto:xx dimensions have traditionally been documented with Min and Max values instead of limits. This practice has been continued for S-3.1 and S-4.1.
Original S-3.1 approved 2004 had editing errors based on imporper display of hidden precision values and in the calculation of metric conversion values.

 

 

 

 G C S F F H P R*
Name of Scale Track Gage Check Gage Span Flangeway Frog Flange at Guard Flange Depth Switch Point Spread (Mech) Railhead Radius

 

 

 Min Max Min Max Min Max Min Max Nominal Min Max Min Max

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:20.3 Inch 2.781 2.842 2.679 2.688 2.568 2.596 0.086 0.092 0.102 0.062 2.547 0.018 0.028
mm 70.64 72.19 68.05 68.28 65.23 65.94 2.18 2.34 2.59 1.57 64.69 0.46 0.71

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:20.3n3 Inch 1.772 1.833 1.670 1.679 1.559 1.587 0.086 0.092 0.102 0.062 1.538 0.018 0.028
mm 45.01 46.56 42.42 42.65 39.60 40.31 2.18 2.34 2.59 1.57 39.07 0.46 0.71

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:32 Inch 1.766 1.805 1.701 1.707 1.630 1.648 0.055 0.059 0.065 0.039 1.617 0.012 0.018
mm 44.86 45.85 43.21 43.36 41.40 41.86 1.40 1.50 1.65 0.99 41.07 0.30 0.46

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:32n3 Inch 1.125 1.164 1.060 1.067 0.990 1.008 0.055 0.059 0.065 0.039 0.977 0.012 0.018
mm 28.58 29.57 26.92 27.10 25.15 25.60 1.40 1.50 1.65 0.99 24.82 0.30 0.46

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:48 Inch 1.177 1.203 1.134 1.138 1.087 1.099 0.036 0.039 0.043 0.026 1.078 0.008 0.012
mm 29.90 30.56 28.80 28.91 27.61 27.91 0.91 0.99 1.09 0.66 27.38 0.20 0.30

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:48n3 Inch 0.750 0.776 0.707 0.711 0.660 0.672 0.036 0.039 0.043 0.026 0.651 0.008 0.012
mm 19.05 19.71 17.96 18.06 16.76 17.07 0.91 0.99 1.09 0.66 16.54 0.20 0.30

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:64 Inch 0.883 0.902 0.851 0.853 0.814 0.823 0.028 0.030 0.031 0.020 0.809 0.006 0.009
mm 22.43 22.91 21.62 21.67 20.68 20.90 0.71 0.76 0.79 0.51 20.55 0.15 0.23

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:64n3 Inch 0.563 0.582 0.530 0.533 0.494 0.503 0.028 0.030 0.032 0.020 0.488 0.006 0.009
mm 14.30 14.78 13.46 13.54 12.55 12.78 0.71 0.76 0.81 0.51 12.40 0.15 0.22

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:87 Inch 0.649 0.663 0.625 0.628 0.599 0.605 0.021 0.023 0.023 0.014 0.594 0.004 0.006
mm 16.48 16.84 15.88 15.95 15.21 15.37 0.53 0.58 0.58 0.36 15.09 0.10 0.15

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Proto:87n3 Inch 0.413 0.428 0.390 0.392 0.363 0.369 0.021 0.023 0.022 0.014 0.359 0.004 0.006
mm 10.49 10.87 9.91 9.96 9.22 9.37 0.53 0.58 0.56 0.36 9.12 0.10 0.15

Fine Scale Options

 

 

Name of Scale

 G C S F F H P
Track Gage Check Gage Span Flangeway Flangeway Guard Flange Depth Switchpoint Spread (Mech.)

 

 

 

 

 Min Max Min Max Max Nominal Min Max

 

 

 

 

 

 

 

 
Fine:HO Inch 0.649 0.665 0.613 0.580 0.040 0.040 0.026 0.605
mm 16.5 16.9 15.6 14.7 1.0 1.0 0.7 15.4

 

 

 

 

 

 

 

 

 

 
Fine:HOn3 Inch 0.413 0.429 0.377 0.343 0.040 0.040 0.026 0.369
mm 10.5 10.9 9.6 8.7 1.0 1.0 0.7 9.4

 

 

 

 

 

 

 

 

 

 
Fine:TT Inch 0.471 0.485 0.441 0.414 0.033 0.033 0.022 0.430
mm 12.0 12.3 11.2 10.5 0.8 0.8 0.6 10.9

 

 

 

 

 

 

 

 

 

 
Fine:TTn3 Inch 0.300 0.314 0.270 0.243 0.033 0.033 0.022 0.259
mm 7.6 8.0 6.9 6.2 0.8 0.8 0.6 6.6

 

 

 

 

 

 

 

 

 

 
Fine:N Inch 0.354 0.360 0.340 0.315 0.025 0.025 0.025 0.327
mm 9.0 9.1 8.6 8.0 0.6 0.6 0.6 8.3

 

 

 

 

 

 

 

 

 

 
Fine:Nn3 Inch 0.250 0.256 0.229 0.205 0.025 0.025 0.025 0.219
mm 6.4 6.5 5.8 5.2 0.6 0.6 0.6 5.6

NOTES:

  1. See Tech-Note TN-1.1.2 (Proto and Fine) for more detail on the Proto Scale dimensions and issues related to building in Proto and Fine scale.
  2. * Note: "R" - railhead top to side radius matches wheel profile flange fillet radius.