49 C.F.R. § 213.143
Frog guard rails and guard faces; gage
(a) The guard check and guard face gages in frogs shall be within the following limits—
| 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 1 track | 4′61⁄8″ | 4′51⁄4″ |
| Class 2 track | 4′61⁄4″ | 4′51⁄8″ |
| Class 3 and 4 track | 4′63⁄8″ | 4′51⁄8″ |
| Class 5 track | 3 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. | ||
| 3 See paragraph (b) of this section. | ||
(b) For any heavy-point frog (HPF) on Class 5 track, the guard check gage may be less than 4′6
(1) Each HPF and guard rails on both rails through the turnout are equipped with at least three serviceable through-gage plates with elastic rail fasteners and guard rail braces that permit adjustment of the guard check gage without removing spikes or other fasteners from the crossties; and
(2) Each HPF bears an identifying mark applied by either the track owner, railroad, or the frog manufacturer that identifies the frog as an HPF.