3/8-16 Rod Coupling Nuts, Stainless Steel 18-8, Plain Finish, Quantity 25 Go to amazon.com Related posts Top 9 coupling nut 3/8 Expert choice for coupling nut 3/8-16 FeatureThread Length 1 1/8"Thread Width 1/2"18-8 Stainless Steel provides strength and offers good corrosion resistance in many environments. DescriptionAcouplingnut also known as extension nut is a threaded fastener for joining two male threads, most commonly a threadedrod, but also pipes.