Brass Brake Line Adapter Male 3/8" NPT To Female 5/8-18 Inverted Flare 3/8" Tubing 1pc Used On Transmission Lines, Radiator Ends, ETC. Match the thread and flare type to the lines being connected. It 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.