5/8 -11 ASTM A563 GRB HVY NUT HDG .020” ASTM A563 GRADE B HEAVY HEX NUT HDG ASME/ANSI B18.2.2 1987 IFI-7 AF 1.031-1.062” TH 0.587-0.631” Tapped Over Size per ASTM A 153 class C