HOb5¼ Track Gauge - Code 83

Track gauge for code 83 rail at a gauge of 18.38mm.  This is the exact HO scale (1:87) version of 5'3" gauge, sometimes known as 'Irish' gauge.  5'3" gauge is used by railways in Ireland, parts of Australia and Brazil, and a handful of other places.  To be consistent with the naming convention for narrow-gauge model railways, the scale could be referred to as HOb5¼, HOb5.25, or HOb63.

The gauge is designed to work with code 83 rail that conforms to NMRA recommended practice RP-15, for example the code 83 rail produced by Micro Engineering.

The gauge has four prongs to hold the rails parallel for ease of laying track.  The prongs are placed more widely apart on one side to spread the gauge slightly on curves.  The widely-spaced prongs go on the outside of the curve.

5'3" gauge is common in Australia, though its prevalence has been reduced somewhat in recent decades as lines have gradually been standardised to 4'8½".

The rail network in Victoria is primarily in 5'3" gauge, with the exception of some interstate lines that are in standard (4'8½") gauge and some shortlines such as the Puffing Billy Railway.

South Australian Railways (SAR) began building track in 5'3" gauge in the 1850s to match the gauge in Victoria.  After observing the success of the less-costly 3'6" gauge in Queensland, SAR opened its first line in 3'6" gauge in 1870.  The SAR network was then built in both 3'6" and 5'3" gauges, with standard (4'8½") gauge added in 1917.  A majority of the network has been converted to standard gauge, but more than 200 kilometres of 5'3" track remain in use.