49 CFR 213.355: Frog guard rails and guard faces; gage.

The guard check and guard face gages in frogs shall be within the limits prescribed in the following table—

Class of track Guard check gage Guard face gage

The distance between the gage line of a frog to the guard line 1 of its guard rail or guarding face, measured across the track at right angles to the gage line,2 may not be less than— The distance between guard lines,1 measured across the track at right angles to the gage line,2 may not be more than—

Class 6, 7, 8 and 9 track 4′61⁄2″ 4′5″

1 A line along that side of the flangeway which is nearer to the center of the track and at the same elevation as the gage line.

2 A line five-eighths of an inch below the top of the center line of the head of the running rail, or corresponding location of the tread portion of the track structure.