Wheel Gauging: Wheel Flange

Wheel flange gauging is the inspection of a wheel's flange - the raised inner lip that projects below the tread and rides against the inside edge of the rail head. The flange is what keeps the wheelset guided on the track, so its height, thickness, and contour are checked against interchange limits during wheel gauging.

What Is Checked

Several distinct condemnable flange conditions are gauged:

• **Thin flange** - the flange has worn down in thickness so it no longer presents enough metal to reliably guide the wheel.
• **High flange** - the tread has worn away while the flange has not, leaving the flange standing proud; a high flange can strike frogs, guard rails, and other track hardware.
• **Vertical flange** - the guiding face of the flange has worn to a steep, near-vertical profile, which raises the risk of wheel climb and derailment.

Why It Matters

Each of these defects degrades the flange's ability to steer the wheel through curves, switches, and frogs, increasing derailment risk. The inspector applies the appropriate flange or wheel-defect gauge to the wheel and reads it against the gauge's pass and condemn references; a wheel outside the limits is condemned. The governing height, thickness, and contour limits are set in the AAR interchange rules and field manual.