A plain nut on which has been assembled a nonremovable washer.
NSN 6685-01-530-3718
NSN 6110-01-317-3780
NSN 6220-01-055-7423
NSN 6320-00-139-1090
NSN 6240-00-573-7514
NSN 5945-00-833-8948
NSN 5950-01-291-1568
NSN 6320-00-371-8335
NSN 5996-00-270-0340
NSN 5905-00-269-5452
NSN 5998-00-575-1118
NSN 5905-01-476-3231