Electronic Code of Federal Regulations:

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 The distance between the gage line of a frog to the guard line¹of its guard rail or guarding face, measured across the track at right angles to the gage line², may not be less than—	Guard face gage The distance between guard lines¹, measured across the track at right angles to the gage line², may not be more than—
Class 1 track	4′6 1/8&inch;	4′ 5 1/4&inch;
Class 2 track	4′6 1/4&inch;	4′ 5 1/8&inch;
Class 3 and 4 track	4′ 6 3/8&inch;	4′5 1/8&inch;
Class 5 track	4′6 1/2&inch;	4′ 5&inch;

¹A 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.

²A line 5/8 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.

§ 213.143 Frog guard rails and guard faces; gage.