Diameter: 1/4 Length: 7/8 Material: Stainless Steel Driver Type: 7/16 Wrench Thread Size: 20 (Coarse) Hardness: 18-8 Type: Coupling Nut A coupling nut is a long nut tapped from each side to meet in the middle rather than all the way through in the same direction used to connect two threaded rods end to end.