This is from the NMRA S-7 Clearances. It states that “NMRA Type II Gages used the Old Time dimensions for Narrow Gauge gages.“. With that in mind since I model in On30, I thought to create gages for O scale – Old Time/On3, Classic and Modern since the NMRA so nicely provided the needed dimensions, On30, On2 and On18 not so much.

Since I have a Prusa I3 MK3 FDM printer I can actually print the gages if I want and share the STL files so others can do the same.

Note: This is just me making my own guesses – since this is a WordPress website people can suggest different ideas and argue against my suggestions/conclusions. To that end I am creating sub-pages for each of the gages. Old Time/On3, Classic and Modern are taken directly from the NMRA page. On30, On2 and On18 will be “calculated/Guesstamated”.

  • Old Time/On3
  • Classic
  • Modern
  • On30 – “Using specially manufactured 16.5 mm (0.65 in) gauge track, scaled at 7 mm to the foot (with appropriately spaced, larger Railroad Tie underneath – United States O scale rolling stock (1:48), it becomes a narrow-gauge track of 2 ft 6 in (762 mm), and is referred to as “On 2½” (or On30, as in 30 inches).1Wikipedia – O scale
  • On2
  • On18
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