#3 Female to #4 Male Expander Fitting Black

The #3 Female to #4 Male Expander Fitting Black from EARLS is a precision hydraulic adapter engineered for custom cooling, fuel, and brake line systems in performance and modified vehicles. This fitting bridges two different port sizes, allowing technicians and builders to transition from smaller #3 (3/16-inch) female connections to larger #4 (1/4-inch) male ports without compromising flow integrity. Whether you're fabricating a custom radiator hose setup, upgrading fuel delivery on a turbocharged engine, or reconfiguring brake lines for a suspension modification, this expander fitting provides the adaptability needed to integrate components with mismatched connection sizes.

Manufactured by EARLS—a brand trusted by professional racers and street builders alike—this fitting features a durable black finish that resists corrosion and integrates seamlessly into modern engine bay aesthetics. The expander design gradually enlarges the flow path, reducing turbulence and pressure drop compared to stepped fittings, which is critical when managing high-volume fuel injection systems or forced-induction cooling circuits. The compact 3.1-inch length and minimal 0.02-pound weight make it ideal for tight under-hood packaging, while the precision-machined threads ensure leak-free connections under demanding conditions including high pressure, thermal cycling, and vibration.

This expander fitting benefits engine builders, fabricators, and DIY enthusiasts upgrading cooling systems on LS swaps, turbo installations, and custom fuel rails where port sizes vary between OEM and aftermarket components. It's particularly valuable in race environments and street performance builds where standardized line routing across multiple systems demands flexible adapter solutions. Installation requires standard hose end crimping tools and proper torque application to avoid thread galling; always use PTFE tape or thread sealant appropriate for your fluid type. Compatible with aluminum and steel hard lines, this fitting delivers reliability whether you're plumbing a mild cruiser or a high-horsepower race car.