They can be more convenient than using a standard hex nut along with a seperate external tooth lock washer.
Lock Nut, 3/8"-16, Steel, Zinc Plated, 50 PK Size: 3/8 inch-16Hex nut with a built in free spinning external tooth lock washerTeeth on lock washer help to lock nut into placeScrews onto a bolt, cap screw or threaded rod of the same thread sizeAlso known as a kep nutThread Type: Coarse, Thread Class: UNC-2BSpecification(s) Met: ASME B1. As with standard hex nuts, they can be installed using a wrench or socket set. The teeth on the lock washer can bite into the surface and help lock the nut into place.1.