Axle and wheel track are commonly measured in millimetres or inches.
It is measured on a wheelset of a railroad car or tram from one wheel flange reference line to the reference line of the other wheel.
[6] The maximum and minimum limits to the differences between the two gauges are usually 111⁄32" and 3⁄8" (9–35 mm).
Model railway elements such as track, rolling stock and locomotives are categorised by their wheel or track gauge.
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