N scale is a popular model railway scale.
O scale (or O gauge) is a scale commonly used for toy trains and rail transport modelling.
O14 is a set of model railway standards for accurately modelling narrow-gauge railways in 1:43.5 (7 mm scale) using gauge track.
On30 (also called On2, O16.5 and Oe) '''gauge''' is the modelling of narrow gauge railways in O scale on HO gauge track in 1:48 scale ratio by American model railroaders, in 1:43.5 scale ratio by British and French model railroaders and 1:45 by Continental European model railroaders (excluding France).
ScaleSeven (S7) is a set of finescale model railway standards for 1:43.5 (7 mm scale) using true-to-prototype track and wheel standards.
In rail transport, track gauge is the spacing of the rails on a railway track and is measured between the inner faces of the load-bearing rails.