49 CFR §229.61

1. (a)A coupler may not have any of the following conditions:
   1. (1)A distance between the guard arm and the knuckle nose of more than 5 5/16 inches on D&E couplers.
   2. (2)A crack or break in the side wall or pin bearing bosses outside of the shaded areas shown in Figure 1 or in the pulling face of the knuckle.
   3. (3)A coupler assembly without anti-creep protection.
   4. (4)Free slack in the coupler or drawbar not absorbed by friction devices or draft gears that exceeds one-half inches.
   5. (5)A broken or cracked coupler carrier.
   6. (6)A broken or cracked yoke.
   7. (7)A broken draft gear.
2. (b)A device shall be provided under the lower end of all drawbar pins and articulated connection pins to prevent the pin from falling out of place in case of breakage.