49 CFR 215.123: Defective couplers.

A railroad may not place or continue in service a car, if—

(a) The car is equipped with a coupler shank that is bent out of alignment to the extent that the coupler will not couple automatically with the adjacent car;

(b) The car has a coupler that has a crack in the highly stressed junction area of the shank and head as shown in the figure below (see figure 2).

(c) The car has a coupler knuckle that is broken or cracked on the inside pulling face of the knuckle.

(d) The car has a knuckle pin or knuckle thrower that is:

(1) Missing; or

(2) Inoperative; or

(e) The car has a coupler retainer pin lock that is—

(1) Missing; or

(2) Broken; or

(f) The car has a coupler with any of the following conditions:

(1) The locklift is inoperative;

(2) The coupler assembly does not have anticreep protection to prevent unintentional unlocking of the coupler lock; or

(3) The coupler lock is—

(i) Missing;

(ii) Inoperative;

(iii) Bent;

(iv) Cracked; or

(v) Broken.