3/8 -16 ASTM A563 GRB HVY NUT HDG .017” ASTM A563 GRADE B HEAVY HEX NUT HDG ASME/ANSI B18.2.2 1987 IFI-7 AF 0.669-0.688” TH 0.341-0.377” Tapped Over Size per ASTM A 153 class C