During the transition period, knuckle couplers on locomotives had a horizontal gap and a vertical hole in the knuckle itself to accommodate, respectively, a link and a pin, to enable it to couple to vehicles which were still equipped with the older Johnston couplers.
Knuckle couplers on locomotives had a horizontal gap in the knuckle. This was during the transition period. Knuckle couplers on locomotives had a vertical hole in the knuckle. This was during the transition period. Itself to accommodate a link and a pin, to enable it to couple to vehicles the knuckle. This is respectively. These vehicles were still equipped with the older Johnston couplers.