49 C.F.R. § 299.333 – Frog guard rails and guard faces; gauge.

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

Table 1 to § 299.333
Track class	Guard check gageThe distance between the gauge line of a frog to the guard line 1 of its guard rail or guarding face, measured across the track at rightangles to the gauge line,2 may not be less than—	Guard face gageThe distance between the guard lines,1measured across the track at right angles to the gauge line,2 may not be more than—
H0-H7	1,393 mm	1,358 mm.
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 14 mm (0.55 inches) 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.