A bent spring metal washer with a centrally located hole. It is designed to exert pressure axially when assembled in place.
NSN 6145-01-425-0491
NSN 6240-00-316-3167
NSN 6645-01-521-8525
NSN 6240-00-484-8148
NSN 6320-01-544-6447
NSN 6135-00-305-2052
NSN 5930-01-123-8583
NSN 5950-01-428-7084
NSN 6320-01-652-3806
NSN 5996-00-466-9781
NSN 5998-01-299-2170
NSN 5905-01-152-2580