Solid Brass Brake Line Adapter Male 3/8" NPT To A Female 5/8-18 Inverted Flare 3/8" Tubing. Used On Transmission Lines, Radiator Ends, ETC. Match the thread and flare type to the lines being connected. is important that both flare type and thread match for a leak-proof connection. SAE Thread Size 3/8 NPT Male, 5/8-18 Female