What does a "high flange" define in terms of height above the approximate line of thread?

In the context of railway mechanics, the term "high flange" refers to the height of the flange of a train wheel relative to the approximate line of the thread. A high flange typically indicates a greater stability and a better ability to maintain alignment on the track, which is crucial for safe and efficient train operation.

The standard definition for a high flange is that it must be 1 1/2 inches or more above the approximate line of thread. This specification ensures that the flanges provide adequate support for the wheels during movement, particularly during curves and when dealing with imperfections on the track. Having a flange of this height is vital in maintaining proper contact with the rail, which aids in preventing derailments and ensuring a smooth ride.

Higher options, such as 2 inches or 2 1/2 inches, would represent increasingly more significant flanges, which may not be standard and could potentially affect the performance and compatibility of the wheels with existing tracks. In contrast, the option of 1 inch does not satisfy the criteria for a high flange, as it is below the recognized measurement of 1 1/2 inches.