Elliptical locking feature id
A soft metal or nonmetal sleeve, designed to mate with a pin-rivet. it may include an external wrenching facility which breaks off at a perdetermined torque to form a head.
NSN 5990-01-272-4091
NSN 5999-00-073-0642
NSN 4140-01-399-0330
NSN 5925-01-641-5779
NSN 5975-01-085-5824
NSN 6240-01-406-5345
NSN 6110-01-104-4777
NSN 5915-00-211-7060
NSN 5835-00-759-1109
NSN 6150-01-382-9621
NSN 5905-00-192-7044
NSN 6620-01-232-8552