The background to Proto scale modelling

The origins of P4

People enjoy the many facets of railway modelling for a whole host of reasons.

Some mainly like running trains, and they buy ready-to-run locomotives, rolling stock, track and structures. Often they are very happy with a “near enough is good enough” approach. That suits them, and they enjoy our hobby as much as anyone else -- railway modelling gives enjoyment to everybody!

Others gain enjoyment by setting themselves challenges. In the 1960s, some railway modellers in the UK, looking at making their models more and more accurate, kept coming back to an uncomfortable conclusion: model railway track and wheels in their scale (4 mm to the foot, or 1: 76.25 scale) just didn’t look the same as in full size. And with many variations among manufacturers the running reliability wasn’t very good either.

The relationship between track and the wheels that run on it is as fundamental in model sizes as in full size. The problem was that in the early decades of the 20th century, it proved impossible to fit electric motors into HO scale models of British locomotives (which were narrower than US locos). The commercial “solution” was to increase the scale from 3.5 mm to the foot up to 4 mm to the foot -- except for the track gauge, which remained at 16.5 mm. This crude adjustment gave what was then called “OO” gauge a distinctly narrow-gauge (4’-3”) appearance. Further, manufacturing standards were not very high and castings were often crude zinc alloy. The specifications or standards for track and wheels were made coarse -- with deep flanges to reduce derailments (or so it was thought) and wide gaps in pointwork -- because mass-market manufacturers wanted their products to stand up to the rigours of handling by children. Importantly, there was no understanding that wheel contour and rail contour were inextricably linked.

A small study group set out to investigate the practicalities of reducing track and wheel dimensions down from full size to scale (scale = a constant proportion of full size, to produce a model correct in all dimensions and detail). It became evident that some compromise would be necessary to accommodate manufacturing tolerances (albeit fine ones) at this scale, but the standards the group proposed were very close indeed to full-scale railway practice.

NEM and P4 wheels compared (cropped)

This photo by the study group contrasted the crude proportions of the European NEM wheel with Protofour wheels, very close to full-size appearance.

The British standard of the time was in between these two extremes. But like NEM, it made no provision for the all-important fillet between the wheel tread and flange, described on
this page.


The integrated standards were called “Protofour” since they were derived directly from the prototype (i.e., full size railways) and were applied to 4 mm scale. This was often shortened to “P4”.

The study group realised that it was essential to apply strict dimensional and quality control to track components and wheels, far beyond the practice of commercial manufacture at the time, and two of its members formed a company that for many years produced the key components. Precision in manufacturing is still the key to why such fine wheel and track standards are so well integrated.

Development of P87

Model railroaders in the US began to take notice of Protofour developments. Their wheel standards had previously undergone much more development than those of the UK, thanks to the [US] National Model Railroad Association, but they were still more coarse than some people wanted. The result was a set of standards derived from a similar process to Protofour standards while reflecting, among other things, the fact that US models were built to a scale of 3.5 mm to the foot, or 1:87.1.

These standards were called “Proto 87”, often shortened to “P87”.

Either / or ...

Models of Australian railways, like those of the US and Canada, have for a long time been to 1:87.1 rather than 1:76.25, so members of our group who model Australian prototype follow P87 standards.

Our members who model UK prototypes follow P4 standards.

We have projects going on in both of these fields of interest. We exist happily side-by-side -- literally, since our new 22-metre building provides space for a P4 exhibition layout along one side and a P87 layout opposite.


'Next' button_w

'Back' button_w