Fifth Wheels 3 2 2 3 1 B 1 4 4 A D C 11/07/94 f310106a A. Locks open. B. Locks closed. C. Kingpin correctly entering the lock. Note how the depressed tongue allows lock halves to close completely around the neck and shoulder of the kingpin. D. Kingpin incorrectly entering the lock. Note how the steel tongue prevents lock halves from closing, preventing false lockup. 1. Fifth Wheel Plate 2. Trailer 3. Kingpin 4. Lockguard Fig. 11.3, Lockguard Mechanism (rear view) 11.4