The use of half / thin nuts as a lock nut is only required in special situations where the bolts are only tightened to snug tight conditions and the joints are subject to vibration that could promote vibration loosening.
The Half/ Thin nut when used together with a Class 8 Hex nut is essentially working as a washer that provides locking and the total strength is generated through the larger Class 8 nut.
There is a common misunderstanding of how the thin nut works that generates requests for Class 8 lock nuts.
The softer the lock nut, the better it works.
