The 7mm Narrow Gauge Association aims to encourage the modelling of
narrow gauge railways at a scale of or around 7mm to 1 foot (1:43)

What is O-9?

The Association encourages narrow gauge railway modelling in all its many forms. One perhaps more specialised scale for a good number of members is 'O-9', using 9mm gauge track in 7mm:ft scale to represent mainly British minor lines built to a gauge of 15in, often termed “minimum gauge” railways. The term originated in describing the narrowest suitable gauge for a practical load-carrying
railway, as originally built and demonstrated by Sir Arthur Heywood at the end of the 19th century.

He was inspired by Spooner’s work on the Festiniog Railway and also 18in gauge industrial railways such as those at Crewe and Horwich railway works, Woolwich Arsenal and Chatham Docks. After demonstrating the potential of 15in gauge railways on his private Duffield Bank Railway in Derbyshire, he subsequently constructed a railway to the same gauge for the Duke of Westminster at Eaton Hall in Cheshire. Other lines were built on other private estates to transport supplies, fuel or timber around, or simply for their owner’s enjoyment. Consequently 15in gauge lines are often called 'estate railways'.


This was also the gauge used by Narrow Gauge Railways Limited when they took over and re-gauged the Ravenglass & Eskdale Railway in Cumbria and the Fairbourne Railway in Wales. 15in gauge was also chosen by Henry Greenly for Captain J.E.P Howey’s Romney Hythe & Dymchurch Railway in Kent using beautiful one third scale main line Pacific locomotives. Other early lines newly created for the leisure market included the Lakeside Miniature Railway in Southport and the Rhyl Miniature Railway. More recently, several new lines have been built, sometimes laid on former standard gauge track beds including the Bure Valley Railway in
Norfolk, the Heatherslaw Light Railway in Northumberland, the Kirklees Light Railway in West Yorkshire, and the Perrygrove Railway in the Forest of Dean. Many of the newer lines have adopted a more 'narrow gauge' style rather than the 'main line in miniature' approach.

O-9 Modelling

O-9 takes advantage of N and OO-9 scale mechanisms which can be used to represent 15-18in gauge prototypes. Likewise commercial N and OO-9 scale track can be used as the permanent way, and can also be modified to replicate prototype track with a bit of research as can be found in the Going Minimum Gauge Handbook from the Association.

Locomotive bodies, wagons and coaches can be obtained through many small manufacturers in 3D printed or kit form. Many of these have been designed to run on standard N scale chassis. A supplier list (not just for O-9) can be found via this link.

A distinct advantage of O-9 scale is the small space required for a layout which can represent a significant part of a prototype railway. Unless you want to run long wheelbase locomotives and bogie coaches, an interesting layout can be built in a very small area.

See the O-9 Gallery page for photographs of recent layouts, locomotives and rolling stock.

If you would like to know more about O-9 scale modelling, a very good place to start is with the Association's Going Minimum Gauge Handbook available from the publications sales. It includes prototype information, layout examples, loco and rolling stock construction, track and alternative gauges, couplings and other handy information.