The society logo over a background of trackwork. For 4mm finescale railway modelling at its very best

The Protofour Manual
Section 2. Standard Dimensions.
2.0. Protofour & Preferred Proto Ratios

PROTOFOUR

 
When the Protofour 4mm/1ft scale standard track and wheel dimensions were finalised by the Model Railway Study Group in March 1966, many modellers in other scales expressed a desire to adopt the Protofour concept of authentic modelling. Investigation by the Group resulted in Proto-standards, and associated data, being computed for sixteen of the scales in common use throughout the world. With the exception of the basic Protofour 4mm/1ft, these scales fall into six groups, each centred upon a nominal track gauge and having variations of scale within each group according to country of origin. Since there were, even then, clear indications that the appeal of the Protofour concept was becoming an international one, a rationalisation of the basic scales was obviously necessary to avoid confusion.

 
Broadly speaking the situation was as follows. British scales are traditionally based on metric equivalents of imperial feet, with track gauges adopted from other countries. As a consequence these track gauges are generally out of scale. Whereas the American scales use inch fractions or decimal equivalents of feet with near scale track gauges, the European scales are expressed as round figure ratios, or proportions, of the prototype and have virtually correct scale track gauges. Furthermore the European series of scales is more evenly spaced, and achieves a near consistent (approximately twofold) area ratio for adjacent steps in the scale series.

 
In attempting to resolve the problem of rationalisation many factors were borne in mind; firstly, the obvious need to retain the Protofour 4mm/1ft scale as the British basis of the Protofour concept. Britain, Australia and New Zealand are joining 90% of the world’s population by adopting a metric system, while the United States and Canada are considering similar changes. In a generation or so imperial-based scales will not only be obsolete, but they will leave an illogical series of decimalised ratios peculiar to this country.

 
It seemed logical, therefore, to suggest the adoption of the European series of round figure ratios, as this also has the advantage of offering internationally accepted track gauge dimensions which are themselves virtually dead scale; the worst case of such rounding up error is only 0.35% in Proto-160. amounting to less than 0.032mm over gauge. Six scales other than the basic Protofour 4mm/ift scale have been selected for adoption as basic scales and these are termed the Preferred Proto ratios. The accompanying table is headed with the basic Protofour standards, followed by the track and wheel dimensions, with tolerances as necessary, for the six preferred Proto ratios. For consistency these dimensions and tolerances are directly proportional to the Protofour dimensions. It is important to emphasise that although the preferred ratios give decimalised metric/imperial feet scales, the provision of conversion tables, charts and prototype information compiled by the Study Group completely eliminatesthe often quoted problem of metrication. One very important aspect of the preferred ratios is that it will be possible for modellers in other than 4mm/1ft scale to continue using their traditional track gauges, but with turnouts and wheels correctly scaled to the appropriate Proto-standard for improved appearance and performance. Research and the development of products to the preferred ratios is continuing within the Study Group and the Protofour Society. Comments and enquiries on any aspect of the standards and their use will be welcomed, and should be addressed to the M.R.S.G., c/o The Editor of Precision, the Journal of the Protofour Society. September 1970 STANDARD DIMENSIONS FOR PROTOFOUR

 

Standard Dimensions for Protofour

 

        mm in
1 Track Gauge TG min. 18.83 0.741
2 Gauge Widening GW max. 0.22 0.009
3 Check Gauge CG min. 18.15 0.715
4 Crossing Flangeway CF max. 0.68 0.027
5 Crossing Flangeway CF min. 0.65 0.026
6 Between Checks BC max. 17.47 0.688
7 Effective Flange EF max. 0.40 0.016
8 Effective Flange EF min. 0.35 0.014
9 Wheel Back to Back BB max. 17.75 0.699
10 Wheel Back to Back BB min. 17.67 0.696
11 Tyre Width TW max. 2.00 0.079
12 Tyre Width TW min. 1.85 0.073
Scale 4mm to lft. (1:76.2)

 

THE PROTOFOUR MANUAL 2.0.(1)

 

PROTO-160 (N-gauge) PROTO-64 (S-gauge)
      mm in
1 TG min. 9.00 0.354
2 GW   0.11 0.004
3 CG min. 8.68 0.342
4 CF max. 0.32 0.013
5 min. 0.31 0.012
6 BC max. 8.35 0.319
7 EF max. 0.19 0.008
8 min. 0.17 0.007
9 BB max. 8.48 0.334
10 min. 8.45 0.333
11 TW max. 0.95 0.038
12 min. 0.88 0.035
Scale 1.905mm to 1ft
      mm in
1 TG min. 22.5 0.886
2 GW   0.26 0.010
3 CG min. 21.69 0.854
4 CF max. 0.81 0.032
5 min. 0.77 0.031
6 BC max. 20.88 0.822
7 EF max. 0.48 0.019
8 min. 0.42 0.016
9 BB max. 21.21 0.835
10 min. 21.12 0.831
11 TW max. 2.38 0.094
12 min. 2.20 0.087
Scale 4.76mm (3/16") to 1ft
PROTO-120 (TT-gauge) PROTO-45 (0-gauge)
      mm in
1 TG min. 12.00 0.472
2 GW   0.14 0.006
3 CG min. 11.57 0.456
4 CF max. 0.43 0.017
5 min. 0.41 0.016
6 BC max. 11.13 0.438
7 EF max. 0.25 0.010
8 min. 0.22 0.009
9 BB max. 11.31 0.445
10 min. 11.26 0.443
11 TW max. 1.27 0.050
12 min. 1.18 0.046
Scale 2.54mm (1/10")  to 1ft
      mm in
1 TG min. 32.00 1.260
2 GW   0.37 0.015
3 CG min. 30.84 1.214
4 CF max. 1.15 0.045
5 min. 1.10 0.043
6 BC max. 29.69 1.169
7 EF max. 0.68 0.027
8 min. 0.59 0.023
9 BB max. 30.17 1.188
10 min. 30.03 1.182
11 TW max. 3.39 0.133
12 min. 3.13 0.123
Scale 6.77mm to 1ft
PROTO-87 (H0-gauge) PROTO-32 (1-gauge)
      mm in
1 TG min. 16.50 0.650
2 GW   0.19 0.008
3 CG min. 15.90 0.626
4 CF max. 0.60 0.023
5 min. 0.57 0.022
6 BC max. 15.31 0.603
7 EF max. 0.35 0.014
8 min. 0.31 0.012
9 BB max. 15.55 0.612
10 min. 15.48 0.610
11 TW max. 1.75 0.069
12 min. 1.62 0.064
Scale 3.503mm to 1ft
      mm in
1 TG min. 45.00 1.772
2 GW   0.52 0.021
3 CG min. 43.37 1.708
4 CF max. 1.62 0.064
5 min. 1.55 0.061
6 BC max. 41.75 1.644
7 EF max. 0.95 0.038
8 min. 0.83 0.033
9 BB max. 42.42 1.670
10 min. 42.23 1.663
11 TW max. 4.76 0.188
12 min. 4.41 0.173
Scale 9.525mm (3/8") to 1ft
© THE MODEL RAILWAY STUDY GROUP 1970
Not to be used or reproduced for any commercial purpose without written permission of the M.R.S.G.