A sixteenth of an inch is the only real difference between traditional O scale track and P48. It isn’t that much but in the 1950s that sixteenth of an inch often meant war between traditionalists and those who saw the potential of closer to scale wheels and a corrected track gauge. One needs to remember that there were few if any across the board standards in the early days and with wheels, it was still the Wild West. Marshall Dillon hadn’t cleaned up Dodge City yet.

P48 started with a desire for functional dual gauge turnouts, with the problem being the different wheel and flange profiles on standard and narrow gauge wheels. The two were basically incompatible.

In the 1950s Norm Buckhart and Dan Ranger, both narrow gauge modelers, were building an On3 model of a D&RG C-16 locomotive. This project led to the discovery of an 1890 Railway Equipment Guide that contained a thorough discussion of prototype wheel profiles and specifications.

This newfound knowledge led to development of the first prototypically accurate narrow gauge model wheels made by Al Henning. Al’s wheels had a tread width of 0.117”, a properly formed fillet between the flange and tread, and a flange depth of 0.028”. Seeing how well Al’s wheels performed, Don Graf had some standard gauge wheels made. They also ran beautifully and were compatible with the narrow gauge flangeways.

This solved the compatibility problems that plagued the construction of dual gauge turnouts. However, attempts to run ordinary standard gauge wheels over the new trackage proved disastrous. The standard flanges hit the spike heads of the smaller code 100 rail of the new dual gauge tracks, which aggravated the traditionalist members of the club where this all took place.

Group politics being what they are, the floodgates of controversy opened and a big disagreement ensued between the narrow gauge modelers and the other club members over which wheel specs to use. In time, the narrow gauge modelers struck out on their own to pursue the finescale wheels and accurate track, thus laying the groundwork for others in the future. Once they discovered that an accurate flange profile would track well for standard gauge, they also decided to complete the picture and use the correct track gauge. Remember, traditional O scale track was and still is too wide, a result of some bastard compromise in the dark ages of the hobby.

P48 Growth
Development of the new wheel and gauge standards grew in fits and starts as more products became available from dedicated individuals who believed in the work. Finally, in the 1980s, after nearly three decades of work to advance finescale modeling standards in quarter-inch scale, a set of specifications for accurate wheel and flange profiles based on scaled down dimensions from the prototype was finally recognized by the NMRA. This also included the accurate track gauge. The new specs became known as Proto 48. The term “proto” was chosen for its applicability to other scales, which also had proto-based movements such as Proto 87 and Proto 64 in HO and S scales respectively.

Modeling Is Modeling
I’ve never quite understood the mythology that has developed around finescale standards. When I was editor of O Scale Trains Magazine, we would get dissenting mail every time we ran P48 material; not a lot but we could always count on some. O scale is hide bound by tradition and many older modelers saw it as a threat of some kind. It’s understandable I guess when you have a lifetime of accumulated stuff that you’re afraid will become obsolete if the new kid gets too popular.

What I still don’t understand is the knee jerk reaction many people have to any form of finescale standard. You can routinely expect declarations of how that stuff will never work, or won’t work for a basement size layout. It’s too fussy, too hard, too expensive, too this or too that. Of course, most of this is nonsense and ill informed opinion. It’s all modeling, regardless of the standard involved. No one objects to the NMRA standards, so what’s the big deal with finescale?

Today, P48 has come into it’s own. You can get started with relative ease but be prepared to enter a different world from the want it, go buy it ease of HO or N. P48 has a good supply of essential products like trucks and wheel sets in a variety of styles and diameters, along with accurate working couplers and even flex track with the correct gauge but you’ll have to do a bit of legwork to find them. Plug and play commercial turnouts aren’t available as yet, and I for one, don’t see that as a hindrance, because modelers who are drawn to this standard are usually experienced and can easily make what they need either from scratch or by using the excellent castings that are available. There are customer builders who offer handlaid turnouts in a variety of frog numbers and rail sizes, so you don’t have to lay your own if you really don’t want to.

Protocraft, run by Norm Buckhart, is the essential source for P48 wheels, trucks and couplers. He also has a beautiful line of limited run brass freight cars and a growing line of steam era decals. Rich Yoder of RY models also has a great line of trucks and Jay Criswell deserves our gratitude for carrying on the Right-O-Way line of track details from the late Lou Cross. (Jay is modernizing the operation by bringing it online.) It’s not an exaggeration to say that working in P48 would be nearly impossible without the resources and supplies these individuals make available.

An excellent online resource is Gene Deimling’s Proto48 Modeler site. Here you’ll find an extensive list of suppliers and inspirational modeling. It presents a compelling narrative for P48 and is included in the links below.


Some Relevant Links


Right-O-Way Products

Proto48 Modeler

Rich Yoder Models

I would be remiss in not mentioning this volume of The Missing Conversation.
The Missing Conversation Vol. 03 From OST Publications


  1. Simon


    An interesting post, and I enjoy the provocative title!

    Fundamentally, adopting “Proto” standards (and in the UK, we use slightly different terminology, but S scale here is Proto:64 as we only have the one, prototypically-derived, standard!) isn’t even about the track gauge, nor is it about the wheel and track standards. It falls into that “world apart” category, for it is a different mindset. It’s a mindset about pushing oneself to create models that get as close to a direct representation of the real thing as possible, and inevitably about applying the concept of maximum (not complete) fidelity to the wheels and track.

    Complete fidelity is impossible. We reduce each dimension of the real thing by a scale factor, e.g. 48, but area reduces by the square of that and volume (and hence mass) by the cube. Some material properties (for example rigidity based on cross-sectional area) may decrease by the square, with respect to the load (mass) decreasing by the cube. Put another way, a styrene girder could be effectively 48 times stronger than in “real life”. This means we are freer to choose materials and techniques in our modelling which cannot be used in the prototype, but conversely that we also need to accommodate the reverse situation. Most model railways are built on much more solid foundations than the prototype, and have much more rigid mechanical assemblies (our engine frames, particularly for steam engines, have virtually no flexibility). This means that things should run more smoothly, but that engines and rolling stock lack and “give” if they encounter bumps and dips. Some form of compensation (springing or beams) therefore helps, and a little more side play needs to be incorporated within rigid wheelbases. And also, unless one is modelling an electrified system and using the overhead wire or third rail to provide power, we don’t power our engines in the same way as the real thing – they are not locomotive engines, and that is the biggest infidelity of all! In my experience, beam-compensation produces better track holding, but properly designed springing not only achieves this, but introduces a smoothness to the ride that helps convey the impression of several tons moving.

    There is a wider picture: track modelled to Proto standards looks more like the real thing, as things like flangeways and guard rails are correctly proportioned and spaced. Slightly more subtly, as sometimes this is hidden in the Stygian gloom underneath the body, things like truck frames are the correct distance apart. 1/4″ scale trucks have to contend not only with the extra 1/16″ or so of track gauge, but also wider wheel treads which require the truck frames to be further apart. The same is true for engines: steam locomotives require the cylinders to be spaced further apart, and the same is truck for the trucks of diesel and electric engines. In the case of model engines, this is not a subtle issue, as it tends to be rather more obvious. To me, that is a very compelling reason for adopting finer standards. Even in 4mm scale, running on H0 track, (00 gauge) there can be problems with outside cylinders, so when one is confronted by the scale 5′ track gauge of North American 0 Scale, the problems must be even worse!

    To anyone who thinks that Proto:48 wheel and track standards can’t work, then perhaps they can explain why H0 and scale (NASG /NMRA) S work, for they are using track and wheel standards very close to Proto:48. They can also explain why they can’t work when standing next to a layout built to these standards? I have operated a friend’s “Scale 7” (UK equivalent of Proto:48) layout at several two-day shows, where the only problems have come from operator error. Including yours truly not cutting the power quickly enough to stop and engine continuing off a turntable and into the ballast!

    An open-minded modeller will always accept that people choose their wheel and track standards for a variety of reasons, and that like the track gauge, this may rule out running stock straight out of the box, or on other modller’s layouts. They will also realise that working to finer mechanical tolerances requires more care (i.e. more time), but that any model railway requires careful, methodical craftsmanship. An open-minded modeller will accept that, even if it means their own models are technically not-to-scale when it comes to issues such as track, wheels, and trucks.

    A closed minded railway modeller will fall into one of two camps. There are those who simply can’t accept that others have different priorities in their hobby as well as life, and who are prepared to balance the time and cost of re-wheeling and hand laying track against the increased time for operating. Yes, if the resources were available, a large operationally-focussed basement empire is perfectly possible in Proto standards, and it would produce spectacular running, too. But if this turns a 20 year project into a 40 year one, many will simply not go down that route. The other camp consists of those who feel that their modelling is somehow inferior: there can be no other explanation for the vitriolic nonsense that appears in print as well as on-line. Well, maybe the first camp of the closed-minded (the scale zealots) hasn’t helped here, in their proselytising fanaticism, but such reactions usually come from a feeling that one is being implicitly or explicitly criticised for being wrong, and that deep down, one feels this to be the case.

    Part of the problem is terminology. We use the words “scale model” to state that an object is not a toy, but an accurate (scale) representation (model) of a real world entity. Without this definition, “fine scale” is meaningless, but with it, it comes “(more) accurate”, with the obvious implication that being scale is nothing more than a substandard model that is closer to being a toy. And toys are for children, not for adults. A good way to wind up many, if not most, railway modellers is to ask them if they are going to “play with their toy trains” rather than “operate a model railway”.

    If I am enjoying myself, then I really don’t care what others think. If I gain satisfaction from activities, then I am not even aware of what others think.


  2. mike

    Goodness Simon, I don’t know where to begin.

    The hardest aspect is conveying how fragmented quarter-inch scale modeling is in the US. Aside from G scale, it’s the only one I’m aware of with two standards for standard gauge track and three different wheel profiles and they’re all essentially incompatible. With each one vying for a share of a very small market, the impact of this has been profound. I think that’s all I’m going to say.


  3. Simon

    I got a bit carried away there!

    Just looked at the NMRA web site to make a comparison between the maximum measurements recommended over the outside faces of the wheels for hi-rail and Proto:48, as this determines how far apart the truck frames need to be as a minimum: clearances may be greater for hi-rail, and this also assumes that the truck frames are to scale width.

    The differences are astounding. The difference in track gauge might be a scale 3.5 inches, but the difference in the recommended maximum “over faces” measurements scales out at 14.16″! That’s 22% over scale, or the equivalent of 1:39 scale. Obviously, this is somewhat reduced for the “standard” NMRA standards, but even if a freight car is to the correct dimensions otherwise, a model released to cater for all three standards and both gauges will need new trucks for P:48, or new bolsters as well as new wheels.

    I understand that Proto standards are not for everyone, but accepting key features which are so far out of scale strikes me as rather lax, to the point where I personally wonder if the model has become a toy?

    Ultimately, if finer standards cannot work – as some insist – then can someone please explain Z gauge?