National Aerospace Standard - Steel Nut, Self Locking, Hexagon | NAS679A4

Self-Locking Nut, Low Height, A" After Base # Indicates All Metal,"W "Indicates Internal Wrenching Feature, "C" Indicates A286 CRES, Silver Plated for 800 ºF, "M" Indicates Dry Film Lubricant for 450 ºF Use.