A plain nut on which has been assembled a nonremovable washer.
NSN 5895-01-502-9765
NSN 5930-00-756-8117
NSN 5965-01-389-0004
NSN 5895-00-847-8935
NSN 2925-01-307-7429
NSN 6650-01-512-9650
NSN 6610-01-536-4056
NSN 5999-01-607-6418
NSN 4140-01-418-0831
NSN 5910-01-633-9963
NSN 5925-01-050-2009
NSN 6150-01-432-1020