Inverted Flare Nut 4pk 5/8-18 for 3/8 Line S/S

The Inverted Flare Nut 4pk 5/8-18 for 3/8 Line in stainless steel from ALLSTAR PERFORMANCE is a critical brake system fitting designed for precision hydraulic and fuel line connections in high-performance automotive applications. This four-pack set provides inverted flare male connectors that create a leak-free seal through compression—a design favored in racing, restoration, and custom fabrication work where fluid integrity under pressure is non-negotiable.

Each fitting features a 5/8-18 thread specification designed to accommodate 3/8-inch hardline tubing, making these connectors ideal for brake systems, fuel injection systems, and cooler lines where standard SAE flare connections are required. The inverted flare design—where the flare cone points inward rather than outward—provides a tighter seal under vibration and thermal cycling, critical for engine bays and suspension-mounted components. Stainless steel construction resists corrosion from road salt, coolant splash, and moisture exposure, extending service life compared to zinc-plated alternatives, particularly in marine-adjacent or high-humidity environments.

Buyers restoring classic muscle cars, building custom brake systems, or upgrading OEM fuel lines depend on accurate, reliable flare nut fittings that maintain pressure without weeping. The four-pack quantity addresses the typical brake system (which may require multiple distribution block connections) or allows spare inventory for field repair. ALLSTAR PERFORMANCE fittings meet SAE J518 Code 61 inverted flare standards, ensuring compatibility with aftermarket brake proportioning valves, master cylinder adapters, and hardline junction blocks commonly found in street rods, race cars, and performance restoration projects.