49 C.F.R. § 230.76
(b) Maximum piston travel. The maximum piston travel when steam locomotive is standing shall be as follows:
| Type of wheel brake | Maximum piston travel (in inches) |
|---|---|
| Cam Type Driving Wheel Brake | 31⁄2 |
| Other forms of Driving Wheel Brake | 6 |
| Engine Truck Brake | 8 |
| Tender Brake | 9 |