I have been known to make arithmetic errors. That said, I get, for 1 1/4" gauge, assuming the prototype is 4'8 1/2" gauge, .2613" per foot. (6.637 mm)
17/64 scale is .265625" per foot (6.7469mm)
7 mm, while larger than either of those, would look best with our wider treads and side frames. I seriously doubt that any manufacturer will consider any of those scales.
That's a good thing for me, and a bad thing for whoever inherits my collection. My 17/64 models have a certain uniqueness that a 700E will never have. Nobody will want them because they do not really match anything else. On the other hand I pull 1/4" scale cars with them and nobody notices until I tell them.
Some early manufacturers would enlarge certain things so that main and side rods would fit. You may note that MTH covers that with off- center piston rods and crosshead guides. There has always been artistic license in our hobby.
