5310-00-124-2121 (3M347L5)
NSN 5310-00-124-2121 (NIIN 00-124-2121) is a single ball sea self-locking nut in Federal Supply Class 5310, Nuts And Washers — a nut having one convex, spherical bearing surface and 6 flat sides. Manufacturer part number 3M347L5 (The Boeing Company, CAGE 76301); also referenced as TLN1020L5N (Fairchild Fasteners Europe - Vsd).
Key specs: 36 to 40 rockwell c hardness; full characteristics table below. NIIN assigned December 1972; DEMIL A (none required); unit of issue EA (each), $3.35 gov standard price; ships at 0.01 lb / 0 cu ft.