1/2 -13 ASTM A563 GRB HVY NUT HDG .018” ASTM A563 GRADE B HEAVY HEX NUT HDG ASME/ANSI B18.2.2 1987 IFI-7 AF 0.850-0.875” TH 0.464-0.504” Tapped Over Size per ASTM A 153 class C