A plain nut on which has been assembled a nonremovable washer.
NSN 6145-00-365-0121
NSN 5945-01-199-8858
NSN 5905-01-183-3818
NSN 6135-00-931-9049
NSN 7035-00-406-0568
NSN 5985-01-207-0097
NSN 6220-01-560-0366
NSN 6135-00-485-7402
NSN 6610-01-438-6896
NSN 5950-01-484-5166
NSN 7035-01-210-0493
NSN 7035-00-868-2640