A plain nut on which has been assembled a nonremovable washer.
NSN 5998-00-204-6452
NSN 2925-01-534-5389
NSN 5920-01-072-6610
NSN 5910-00-118-5945
NSN 5945-00-349-4212
NSN 5905-01-260-2804
NSN 5920-00-279-6584
NSN 6130-00-082-2633
NSN 5999-01-063-6189
NSN 6105-00-123-3018
NSN 6645-01-555-4356
NSN 5910-01-298-8920