Dates back to railway days probably? Some lines had smaller track widths, so new bogies needed to be used for the ongoing connection. In Australia for instance, at Federation in 1901, there were different width guages in EVERY state! Nuts!

Next month I fly UA 997 ORD to Chile. BUT planes change guage(ie equipment changes) at MIA, hard to see unless you study the paper timetable.

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~ Glen ~