After the Civil War, the economic recovery of the southern United States hinged on trade with the North and moving goods westward via the railroad. But there was a problem. Tracks in the South had been built with a gauge (or track width) of 5 feet but the majority of tracks in the North had a 4-foot 9-inch gauge (more or less).
So after much planning, over a concentrated two-day period in the summer of 1886, the width of thousands of miles of railroad track (and the wheels on thousands of rail cars) in the South was reduced by three inches.
Rolling stock, too, was being prepared for rapid conversion. Contemporary accounts indicate that dish shaped wheels were provided on new locomotives so that on the day of the change, reversing the position of the wheel on the axle would make the locomotive conform to the new gauge. On some equipment, axles were machined to the new gauge and a special ring positioned inside the wheel to hold it to the 5-foot width until the day of the gauge change. Then the wheel was pulled, the ring removed, and the wheel replaced.
To shorten the axles of rolling stock and motive power that could not be prepared in advance, lathes and crews were stationed at various points throughout the South to accomplish the work concurrently with the change in track gauge.