Rail gauge is the distance between the inner sides of the two parallel rails that make up a railway track. Sixty percent of the world's railways (prototype 1:1) use a gauge of 1435 mm (4 ft 8½ in), which is known as the standard or international gauge. Gauges wider than standard gauge are called broad gauge, those smaller than standard narrow gauge. [source: Wikipedia]
Some common model railway scales and their corresponding track gauges.
Scale in mm/ft
Track gauge (mm)
You have Hornby Set track so it is OO scale and 16.5mm track gauge.
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