What is “On2”?- plus NMRA Standards


The picture above, taken at Edaville, Massachussetts shows typical Maine Two Foot style track and rolling stock amid a collection of other gauged items.

What is “On2”? By customary US model railroad terminology, On2 is the term used to denote the modelling of two foot (narrow) gauge railways in American O scale (1/4″ scale or 1:48th).

As used in these FAQ’s, it means modelling the Maine Two Footers in American O scale (1/4″ scale or 1:48th), resulting in a nominal model track gauge of 0.500″ (half an inch).

Is “On2” P48, Proto 48 or Finescale? No, not according to current NMRA definitions or Standards.

Whilst the actual nominal track gauge modelled is an accurate translation of the prototype practise by the scale, the other track and wheel standards are not derived from prototype practise as required by current NMRA definitions.

Click here to view the NMRA Proto Scales pdf TN 1 1 2 for S-3.1 and S- 4.2 which gives a listing of proposed dimensions for Proto Scales track and wheel standards – note the absence of On2!

View the NMRA documents which do list On2 dimensions for further information;-

Click here to view NMRA S 1.2 – General standard scales, which gives a listing of modelling scales and the basic track gauge used.

Click here to view NMRA S 3.2 – Scale track, standard scales, which gives a listing of track dimensions controlling pointwork etc.

Click here to view NMRA S 4.2 – Scale wheels, which gives a listing of mounted wheel dimensions.


Written by Terry Smith 13-Aug-2013, updated 03-12-2013, 01-05-2016, 20-08-2016 and 08-February-2017.

1 thought on “What is “On2”?- plus NMRA Standards

  1. Pingback: On2 Mounted Wheel Standards | The Maine On2 FAQ

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